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Different Earth OrbitsBack to Top


There are more and more artificial satellites and space probes rotating around the Earth in space and the numbers are growing. Do you wonder why they do not collide at all?

Actually, there are different Earth orbits in space. Each artificial satellite orbits on separate orbits based on its purpose. The distances between each orbit and the Earth vary, so the satellites do not collide with each other.

Artificial satellites, space telescopes and the International Space Station rotate around orbits including the Low Earth Orbit, Medium Earth Orbit, Geostationary Orbit and Lagrange point ... Why are there so many different orbits? The answer is that each orbit has its characteristics and that satellites and space telescopes choose their orbits for them to function. After launching, they operate in their respective orbits.

What are the features of different orbits? Where are the weather satellites, communication satellites and global positioning satellites that we often use in our daily life? If you want to know more, stay tuned to our posts!

Different Earth Orbits

Published on 2 September 2021

Mutual eclipse and occultation of Jupiter's moons on 22 AugustBack to Top


We'd waited three years for the serial phenomena of Jupiter's moons on 15-16 August. Oops… it was overcast.

With a bit of luck, we successfully observed three individual Mutual Phenomena on 22 and 23 August.

The two events that appeared on the night of 22 August are quite special. First, Ganymede eclipsed Europa (i.e., Europa entered Ganymede's shadow). Then Ganymede occulted Europa (i.e., Ganymede blocked Europa) before Europa leaving Ganymede's shadow. The whole process lasted about 1.5 hour.

We made astronomical photometric observations during that time.

The first image is the light curve of the overall brightness of Europa and Ganymede. Preliminary analysis shows that there is a gradual decrease of light (up to about 35%) during the eclipse. When the occultation ended, the overall brightness resumed. Look closer, there is a bump near 22:45. That amount of small (2-3%) brightness increase was attributed to the short-lived Europa when it was leaving Ganymede's shadow but was partially blocked by Ganymede.

The observations of mutual eclipses and occultations allow us to obtain high-precision position and relative motion of moons, to improve their dynamical models, understand tidal effects and even shed light on their internal structure. More works are needed to analyse the light curve.

Mutual eclipse and occultation of Jupiter's moons

Mutual eclipse and occultation of Jupiter's moons

Published on 30 August 2021

Infrared AstronomyBack to Top


Infrared thermometers here, infrared thermometers there. Under the pandemic, infrared thermometers are everywhere. Besides measuring temperature, can you think of other uses of infrared? Actually, infrared is important in astronomy!

Astronomers use infrared telescopes and detectors to observe the infrared Universe that is invisible to human eyes which can only see visible light. That "invisible" Universe includes some relatively cold and dim celestial objects and protostars situated in dense gas and dust. Moreover, infrared astronomy can help us study the young Universe and shed some light on other mysterious.

What infrared telescopes are out there? Some of the observatories on Mauna Kea in Hawaii and the Atacama Large Millimeter/submillimeter Array (ALMA) in Chile can detect infrared. As water vapour in the Earth's atmosphere absorbs infrared, infrared telescopes are located in high altitudes and dry places. In fact, it is better to launch telescopes into space so they are not affected by the atmosphere like on the ground. Spitzer Space Telescope and the to-be-launched James Webb Space Telescope are infrared space telescopes.

Are you ready to be on the astronomers' track and use infrared to explore the origin of the Universe?

Infrared Astronomy

Infrared Astronomy

Infrared Astronomy

Infrared Astronomy

Infrared Astronomy

Infrared Astronomy

Infrared Astronomy

Published on 18 August 2021

Serial phenomena of Jupiter's moons (2)Back to Top


We mentioned on 29 July that Jupiter is special this year. There are a couple of Mutual Phenomena between Galilean moons around August. Still, not all are observable in Hong Kong (e.g., Jupiter is below the horizon when the events happen). Some of them are not particularly interesting because only one or two phenomena happen within the same night. For example, the occultation and then the eclipse of Europa by Ganymede manifested in the small hours of 9 August (HKT, same below).

However you don't have to be disappointed! You may look forward to the serial phenomena of Jupiter's moons during 15-16 August. From around 7 pm (Jupiter rises) to 3 am, a series of moons' transit, eclipse, occultation and Mutual Phenomena happens that night. Multiple phenomena even co-occur sometimes!

To observe the above phenomena, you need an astronomical telescope of 20 cm aperture or more, with at least 200 times magnification, and a very stable atmosphere.

Online version of the "2021 Astronomical Events" special exhibition:

Computer simulation (the positions of Jovian surface features such as the Giant Red Spot can differ from reality):

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Published on 13 August 2021

Serial phenomena of Jupiter's moons (1)Back to Top


Jupiter is the biggest planet in our Solar System. Its four largest moons (Io, Europa, Ganymede, Callisto, also named GalileanMoons) are orbiting around Jupiter in different orbits. Phenomena such as "transit", "eclipse" and "occultation" occur fairly often as the relative positions of the Sun, the Earth, Jupiter and Galilean moons change.

2021 is a bit special for Jupiter. It is spring for Jupiter and rare "MutualPhenomena" between Galilean moons would be possible. You can understand the orbits and the phenomena with an everyday example: a roundabout.

The orbital planes of the Galilean moons are almost on the same plane (the road surface of the roundabout), and the inclination of the moon's orbital plane will vary by plus or minus three degrees as Jupiter revolves. In Jupiter's winter or summer, it is like we watch the roundabout from the footbridge looking at the moons' orbit from above; in Jupiter's spring (2021) or autumn, it's like we watch the roundabout on the road where the moons' orbits are on the same plane to our view, resulting in obstructing of vehicles (moons).

Some of the mutual phenomena would be observable (via a large telescope) in Hong Kong near mid-year this year. A series of transit, eclipse, occultation, mutual occultation and eclipse will happen within a few hours on 15-16 August. We will introduce it in detail soon. Stay tuned!

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Serial phenomena of Jupiter's moons

Published on 29 July 2021

Conjunction of Venus with Mars today (13 July)Back to Top


Did you see the grouping of Mars, Venus and the Moon yesterday?

Didn't see it? It's ok, let me share the photo taken yesterday with you.

Don't be disappointed if you missed the chance yesterday. Venus and Mars have been slowly moving closer together all month long and they finally culminate in their closest meeting today! If the weather permits, look for Mars and Venus sitting low over the western horizon at around 8 pm this evening.

Venus is the brightest star low in the west and Mars is the dimmer red star to its left. It is easier to see them together with a pair of binoculars.

Welcome to share your photos in the comment field below.

Conjunction of Venus with Mars today

Published on 13 July 2021

Grouping of Mars, Venus and the Moon today (12 July)Back to Top


If the weather permits, looking at the low altitude to the west around 8 pm this evening, you can see Mars, Venus and the Moon at the same time.

Next to the Moon is Venus, which is the brightest star in the field. Further left to Venus is a dimmer red star - Mars.

Welcome to share your images in the comment field below.

Grouping of Mars, Venus and the Moon today

Grouping of Mars, Venus and the Moon today

Published on 12 July 2021

Odd Radio CirclesBack to Top


"Look, that star is so bright!"

Have you ever discovered something bright in the sky and wonder whether that is an airplane, a satellite or a… UFO? Recently, a group of astronomers from Sydney faced a similar problem. They found four "Odd Radio Circles (ORCs)" using radio telescopes. ORCs are roughly circular with bright edges and they are emitting radio waves. ORC's characteristics cannot be explained by known celestial objects. What do you think an ORC is? Let's become a detective to infer the identity of ORCs with a "boldly hypothesise, carefully verify" ScientificMindset.

Possibility 1, Imaging Artefacts
When calibration errors happen in a telescope, a bright ring may form around sources. However, ORCs are observed using two separate, independent telescopes. Well… ORCs are probably not imaging artefacts.

Possibility 2, SupernovaRemnant
When the lives of some stars come to an end they blow themselves up by throwing part of their mass into space called supernova explosions and forming circular remnants. But according to our understanding of supernova remnants, there is only a 0.0021% chance that a supernova remnant would appear in the locations of ORCs. This suggests that ORCs are very unlikely to be supernova remnants.

Possibility 3, RingGalaxy
Some galaxies such as the Cartwheel Galaxy in Sculptor look like a wheel. But those galaxies always emit visible light. That is a huge difference between ring galaxies and ORCs as ORCs only emits radio wave.

Possibility 4, ……
Possibility 1000, ……

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." stated by Sherlock Holmes. If you would like to know more about ORCs, please check our latest issue of HKSpM Newsletter (July – September 2021).

Supernova remnant SNR 0509-67.5 in Doradus
Supernova remnant SNR 0509-67.5 in Doradus
Image credit: NASA, ESA, and the Hubble Heritage Team (STScI/AURA)

Ring galaxy Cartwheel Galaxy in Sculptor
Ring galaxy Cartwheel Galaxy in Sculptor
Image credit: ESA/Hubble & NASA

Published on 5 July 2021

New photos on Martian auroras, signs of black hole-neutron star coalescencesBack to Top


Recently, the Emirates Mars probe Hope captured Martian auroras in ultraviolet light.

The formation of aurora is related to solar wind. Charged particles of solar winds are attracted by the planet's magnetic field, then they interact with the atmospheric gases and light is emitted. The Earth's magnetic field directs charged particles to the polar regions producing auroral ovals at high latitudes. The auroras photographed by the Hope probe are highly structured discrete auroras at various altitudes not confined to higher altitudes. The reason is that Mars does not have a global magnetic field, but it has localised patches of magnetic field that originated from minerals on the surface. Solar wind's charged particles are funneled down to the patches and excite oxygen, forming auroras in ultraviolet light. This discovery helped us to understand the Martian atmosphere and mineral distribution.

On the other hand, astronomers detected gravitational waves triggered when black holes and neutron stars collide for the first time.

BlackHoles and NeurtronStars are compact objects formed after the deaths of massive stars. According to Einstein's GeneralRelativity, gravity produces Gravitational Waves which can be pictured as waves that ripple out across the water surface. When compact objects orbit each other or even merge, powerful gravitational waves are created. LIGO had detected gravitational waves from the black hole-black hole or neutron star-neutron star collisions. This is the first time gravitational from black hole-neutron star coalescences were detected. The observations help us to study the neutron star-black hole binaries.

New photos on Martian auroras, signs of black hole-neutron star coalescences
Image credit: Emirates Mars Mission; Carl Knox, OzGrav-Swinburne University

New photos on Martian auroras, signs of black hole-neutron star coalescences
Image credit: Emirates Mars Mission; Carl Knox, OzGrav-Swinburne University

Published on 3 July 2021

The Most Ancient Spiral Galaxy Ever SpottedBack to Top


On a usual workday at the space museum…

My friend asked: When will you bring me to space?
My mom asked: I was once watching the alien autopsy on TV. Is it true?
My kid asked: How many stars are there in the sky?
A student asked: Dark matter? Dark energy? Black hole?
The public asked me: When will our Sun die?
And…is there an end to the Q & A session?

Takafumi Tsukui, a graduate student of The Graduate University for Advanced Studies, SOKENDAI, and his mentor, Professor Satoru Iguchi, uncovered the oldest spiral galaxy BRI 1335-0417. Their findings were published in the journal "Science" last month.

BRI 1335-0417 galaxy existed 12.4 billion years ago when it was just about 1.4 billion years after the Big Bang. The research team analysed the data of the detection of emission from Carbon ions in the galaxy BRI 1335-0417 by the Atacama Large Millimeter/Submillimeter Array (ALMA) telescope. The rotating disk of this galaxy is revealed clearly in the image mapped from the data (image attached). The team also derived that the spiral arms are part of the galaxy structure from its rotating speed.

Scientists generally believe that spiral galaxies take time to evolve, but now they have discovered this giant spiral galaxy formed just within 1.4 billion years after the Big Bang. It could help understand the formation and evolution of galaxies and stars in the Universe. Whether this galaxy will eventually become a giant elliptical galaxy or remain a spiral galaxy for a long period of time is still cloaked in mystery (we will have to wait another 12.4 billion years to know what it looks like now!), nevertheless, with the advancement of observation technology, we shall see and discover more in future.

Astronomy and cosmology are subjects that come with endless questions and discoveries. Even though we can search for the questions and answers within the boundary of the observable Universe, there are still over 95% of the matter in the Universe that remains unknown to us (including dark energy and dark matter). Everything that we can see or observe, including our Earth, stars, planets, galaxies, etc., account for less than 5% of the matter in the entire Universe. With the launch of the new space telescope and enhancement of computing power, what more and how much further we will see?"

After writing this article...let me just continue working on answering enquires.

The Most Ancient Spiral Galaxy Ever Spotted
Image created from the data of emission from Carbon ions in the BRI 1335-0417 galaxy detected by the Atacama Large Millimeter/Submillimeter Array (ALMA) telescope. (Image credit: ALMA / ESO / NAOJ / NRAO / T. Tsukui & S. Iguchi)

Published on 28 June 2021

Why eclipses usually come in pairs?Back to Top


Last time, we said that SolarEclipses and LunarEclipses usually come in pairs. For instance, the lunar and the solar eclipses occurred on 26 May and 10 Jun 2021 (not visible in Hong Kong) respectively are a pair. But why?

The paths of the Sun and the Moon on the celestial sphere cross each other at an angle of about 5 degrees and have two intersections. When both the Sun and the Moon move near the intersection at the same time, two bodies are almost on the same line in space, it is likely for the Moon to block the Sun seen on the Earth, i.e. a solar eclipse. Similarly, the Earth's shadow may cast on the Moon when the Earth is in the middle of the Sun and the Moon near the intersection, a lunar eclipse occurs.

The positions of the intersections (nodes) on the celestial sphere are not fixed but slowly shift westward. For example, 15 days after the lunar eclipse on 26 May, the Moon came in between the Sun and the Earth. A solar eclipse occurred on 10 June because they were still around the intersection. Another 15 days after the solar eclipse, even though the Moon orbited to the Earth's dark side again, a lunar eclipse did not occur because the Moon is away from the intersection. Similar for a solar eclipse. Therefore lunar and solar eclipses usually occur in pairs. Can you think of otherwise?

Published on 25 June 2021

"Great Dimming" of BetelgeuseBack to Top


Betelgeuse is a reddish bright star in the constellation Orion. It was abnormally fading in late 2019 and early 2020. After in-depth study, astronomers published a latest research paper and several images taken by the Very Large Telescope of the European Southern Observatory last week, revealing the brightness variations of Betelgeuse clearly.

On the far left was the image of Betelgeuse taken in January 2019, showing the normal brightness of the star. The remaining three images were taken in December 2019, January 2020 and March 2020 respectively. The brightness variations in the southern hemisphere of Betelgeuse can be seen.

Astronomers suggest that Betelgeuse ejected a large gas bubble. As its surface region cooled down after, the temperature of the ejected gas decreased in space and a dark solid dust veil was formed by condensation that blocked a portion of light from the southern hemisphere of the star, causing to the "Great Dimming" that lasted for few months.

"Great Dimming" of Betelgeuse
Photo credits: ESO/M. Montargès et al.

Published on 23 June 2021

The Dark Spots on NeptuneBack to Top


When we talk about planetary spots in the solar system, you may come up with the famous Great Red Spot on Jupiter. However, do you know that the planet Neptune also has some dark spots?

The dark spots on Neptune are some giant storms. They can last for years after they appeared. Astronomers have observed several dark spots in the past thirty years. These dark spots would appear at mid-latitude regions and remain stable due to the Coriolis force generated by the rotation of the planet. Then, they would migrate towards the equator and collapse as the Coriolis effect weakened. A new cycle would appear after a few years.

The current dark spot was discovered by the Hubble Space Telescope on the northern hemisphere on Neptune in 2018. In the subsequent observations, astronomers surprisingly found that the spot had changed its common southward motion to an abnormal northward motion. At the same time, a small isolated dark spot was found in a region closer to the equator. Some astronomers speculated that this small dark spot may be originated from the disruption of the big dark spot, and stopped it from moving towards the equator. Since the observation data is limited, the relation between these two spots and the direction of the motion is still unclear.

The Dark Spots on Neptune
Photo credits: NASA, ESA, STScI, M.H. Wong (University of California, Berkeley), and L.A. Sromovsky and P.M. Fry (University of Wisconsin-Madison)

Published on 21 June 2021

Shenzhou-12 manned spaceflight missionBack to Top


Three Chinese astronauts Nie Haisheng, Liu Boming and Tang Hongbo will soon travel to the Chinese space station Tianhe core module in low Earth orbit. They will stay there for three months, which is the longest mission in the Chinese manned spaceflight program.

China is constructing a space station actively. There are 11 launch missions planned across 2021-2022, including 3 space station modules, 4 cargo spaceships and 4 manned spaceflight missions. Now, the Tianhe core module has docked with the Tianzhou 2 cargo in orbit, waiting for the three astronauts to stay.

This manned mission includes two rounds of extravehicular activity, and involves a number of tasks related to space living and technology experiment, such as robotic arm operation, space medicine, in-orbit construction, and more. In this mission, the commander Nie Haisheng and astronaut Liu Boming have completed two spaceflight missions and one spaceflight mission in the past respectively, while it is the first time for Tang Hongbo to enter into space. Each astronaut has received over 6,000 hours of training and they are ready to open a new chapter in the construction of China's long-term space laboratory.

Shenzhou-12 manned spaceflight mission
Image Credit: "我們的太空" 新媒體中心

Shenzhou-12 manned spaceflight mission
Image Credit: "我們的太空" 新媒體中心

Shenzhou-12 manned spaceflight mission
Image Credit: "我們的太空" 新媒體中心

Published on 16 June 2021

Images of Chinese Mars missionBack to Top


The China National Space Administration released the first batch of scientific images of "Tianwen-1" Mars mission on 11 June. The images include panoramic 360 shot of the landing site and the images of the landscape, the lander and the "Zhurong" rover.

Scientific images (China National Space Administration, textual content in Chinese only):

Recently, NASA's Mars Reconnaissance Orbiter captured Tianwen-1's landing site and spotted the lander and the rover.

The rocket of the Tianwen-1 spacecraft was launched from the Wenchang Spacecraft Launch Site on 23 July last year. The spacecraft successfully landed on Utopia Planitia on 15 May this year. The mission aims to complete orbiting, landing and roving in one single mission.

Images of Chinese Mars mission
Mars Reconnaissance Orbiter image credit: NASA/JPL-Caltech/University of Arizona

Published on 13 June 2021

Eclipses usually come in pairsBack to Top


26 May and 10 Jun 2021
19 Nov and 4 Dec 2021
1 May and 16 May 2022
What's so special about these dates?

26 May*, 19 Nov 2021* and 16 May 2022: lunar eclipses
10 Jun, 4 Dec 2021 and 1 May 2022: solar eclipses

They are the dates of SolarEclipses and LunarEclipses! Why eclipses usually come in pairs? Stay tuned!

Remark: Dates are in Hong Kong time. In Hong Kong, only the lunar eclipses with * are/were visible while all solar eclipses cannot be seen.

Eclipses usually come in pairs

Published on 11 June 2021

The Sun & the Solar TelescopeBack to Top


The Sun usually appears as an old man with a zigzag-shaped orange-yellow face in drawings. In fact, nothing wrong about depicting the Sun as an old man because he is 4.6 billion years old! How do you draw the Sun? Share your fantastic drawing in the comments!

By the way, what is the actual color of the Sun? What are the jagged edges?

To protect our eyes, we should not attempt to answer by looking directly at the Sun. Besides the previously mentioned solar filters, we can also observe the Sun with a solar telescope. The SolarTelescope system at the HKSpaceMuseum is a "heliostat" specially designed for observing the Sun. The system consists of three solar telescopes equipped with specially-made filters that use white light, Hydrogen-Alpha (with a wavelength of 656.3 nm) and Calcium K (with a wavelength of 393.3 nm) passbands to observe the Sun.

The Sun is the closest star to us, and its surface is constantly changing under the influence of factors such as rotation and magnetic fields so it's different every day! By observing the sun, scientists can understand more about the structure and evolution of stars. If you would like to observe the Sun safely, come and visit the Space Museum exhibition hall, or visit the Museum's website, to watch the real-time image of the solar telescope to see what is special about the solar surface! If you are lucky, you might see sunspots and zigzag-shaped prominence!

Webcast of the Solar Telescope images:…/SolarTelescope/SolarTelescope.html

The Sun & the Solar Telescope

The Sun & the Solar Telescope

The Sun & the Solar Telescope

The Sun & the Solar Telescope

The Sun & the Solar Telescope

The Sun & the Solar Telescope

Published on 9 June 2021

Supernova Remnant in the Small Magellanic CloudBack to Top


This picture shows a supernova remnant captured by the Hubble Space Telescope. It is located in the Small Magellanic Cloud galaxy, which is about 200,000 light years away. On the scale of the universe, this supernova was considered to be a very close one. Astronomers estimate that the supernova was appeared about 1,700 years ago, it would have been observable to the naked eye from the Southern Hemisphere.

The materials ejected from the supernova are moving at different speeds and directions. The blue part in the picture represents the materials moving toward us, and the red part is the materials moving away from us. Data from the Hubble Space Telescope show that these materials are spreading from the explosion site at an average speed of 3.2 million kilometres per hour. With such speed, we can travel to the Moon and return in just 15 minutes!

Supernova Remnant in the Small Magellanic Cloud
Image credit: NASA

Published on 4 June 2021

Coffee Dreams in SpaceBack to Top


What do you think drinking coffee from space should feel like? Unlimited igable shots with our Earth as background and enjoying sunrise and sunset every 90 minutes?

Drinking real coffee in space is the holy grail of astronauts and terrestrial engineers that have gone through multiple breakthroughs.

Earlier coffee was the freeze-dried kind, however, if you like your coffee with milk and sugar, they need to know the exact ratio you like beforehand and then premix everything in the lab for your onboard journey. Not only you have to decide on which flavors and with or without milk before your journey, you can't even drink in a cup. Microgravity environments make drinking coffee from a normal cup impossible. You either have to drink from a pouch or stick your tongue in the scorching liquid.

Could you brew your own coffee and do a pour over? Well no...before the ISSpresso, brewing was a daunting task as coffee grounds are hazardous in space and you can't possibly drip your coffee by pouring water. ISSpresso is a machine designed to brew espresso in space from pods, not very unlike the kind we have on Earth. Together with the development of a new Space Cup which astronauts can drink through capillary action, that was the sacred moment when real coffee was experienced in space and in the process we gained invaluable knowledge on fluid dynamics in space that would help future explorations.

Merely a cup of coffee? Think twice when you sip on your favourite drink!

Coffee Dreams in Space
Image credit: NASA

Coffee Dreams in Space
Image credit: NASA

Coffee Dreams in Space
Image credit: NASA

Published on 3 June 2021

Eating in SpaceBack to Top


Eating is a piece of cake for us earth-bounded terrestrials, but it is not that easy for astronauts. How can astronauts eat in space where it is difficult just to stand still?

First of all, you have to prepare them. There are different preparing methods for different space food. Astronauts add water to dehydrated food (hot and cold water are available on the International Space Station) and use food warmers to reheat food.

In the weightless space, food would not stay on the table stably. Therefore, after preparing meals, astronauts need to fix the food and cutleries on trays or tables to prevent them from floating around. Tables and trays have magnets or straps to attract or tie cutleries such as knives, forks and spoons, and food. Astronauts also need scissors to open food packages. Astronauts can then use seat belts to secure themselves on chairs to sit down and eat.

To prevent food crumbs and bits flying around, some space foods are cut in bite-size so that astronauts can eat them in one bite to avoid producing bits. When astronauts drink beverages, soups, jams, etc., they squeeze them gradually into their mouths from the pouches.

Do you want to try how astronauts eat in space? Let's make space pudding! First, add pudding powder into a Ziplock bag and add drinking water (just like astronauts adding water to dehydrated food!). Then, seal the bag and mix the ingredients by squeezing the bag until they are even. Refrigerate until ready to serve. When you want to eat, cut off a corner of the Ziplock bag, squeeze the pudding into your mouth or on a spoon (no flying around though), this is what eating pudding in space is!

Eating in Space
Image credit: NASA

Eating in Space
Image credit: NASA

Eating in Space
Image credit: NASA

Eating in Space
Image credit: NASA

Eating in Space
Image credit: NASA

Eating in Space
Image credit: NASA

Eating in Space
Image credit: NASA

Published on 31 May 2021

Tianwen-1 has landed on MarsBack to Top


Tianwen-1 of China has just landed on the Utopia Planitia in the northern hemisphere of Mars. Zhurong rover has parted ways with the lander and will start its exploration.

The Mars mission of China has started when Tianwen-1 was launched in July 2020 and arrived at Mars in February 2021. The mission aims to orbit and land on Mars to collect data about the Martian landscape, soil characteristics, atmosphere and magnetic fields. It helps us to deepen our understanding of our red neighbour.

Tianwen-1 has landed on Mars
Image credit: NASA/JPL

Published on 16 May 2021

Making Space FoodBack to Top


Evolved from a toothpaste-like texture, the space food now are the research and development efforts over the decades.

Space food needs to have a long shelf life, can be eaten directly, or can reheat in the package. Due to the high cost of sending loads to space, space food has to minimise their weight and storage space, extend shelf life and be convenient to eat. Space food processing includes ionising radiation, dehydration (heat drying and freeze-drying), and the retort process.

The growth of microorganisms is the reason behind food spoilage. The above processing methods can inhibit the growth of bacteria (they need water) or directly kill the bacteria, hence the shelf life of food is extended.

Are these food processing methods exclusive to preparing space food? No! Different preservation methods are employed to extend the shelf life of the everyday food we buy. For example, instant coffee and dried vegetables in cup noodles are freeze-dried, canned foods are sterilised under high temperature and they can be kept for a long time.

Although we may not have a chance to taste real space food, we can make a simple version of space food at home! Freeze-dried food can be made in the home kitchen. Adjust the freezer to the highest power, cut the food (such as fruit) into pieces and place them on a metallic plate and put it in the freezer for 2-3 weeks, you will get freeze-dried food like space food!

NASA is researching on space food suitable for long-term missions. What do you think the future space food would be?

Making Space Food
Image credit: NASA

Making Space Food
Image credit: NASA

Making Space Food
Image credit: NASA

Making Space Food
Image credit: NASA

Making Space Food
Image credit: NASA

Published on 12 May 2021

Space food in different countriesBack to Top


Have you ever imagined that you can eat sushi and pizzas in space? Different cuisines we usually eat, like Chinese, Japanese or American food, appear on the astronaut's menu!

When you cannot go back home for a few months (missions on the International Space Station (ISS) last for about 6 months each time), you must miss the food in your country! There is a variety of space food on the ISS. Menus are selected according to the palates and habits of different countries so that astronauts of different nationalities can enjoy food from their hometowns. NASA's space food includes nuts, peanut butter, chicken, beef, seafood and brownies. Japan Aerospace Exploration Agency (JAXA) provides Japanese ramen, sushi, miso soup and curry to astronauts. Russian astronauts have borscht, fish and goulash. Chinese astronauts have Chinese cuisines like Gongbao chicken, Yuxiang pork and Eight Treasure rice.

Not all food can be eaten in space. Bread is one of them as it has crumbs. These crumbs can damage the devices in the ISS or cause them to malfunction when the bits are flying around in the ISS or choking the astronauts. For the astronaut ice cream, you may have seen or even tried it, but it has never been flown to space because they have crumbs. Astronaut ice cream is different from the ice cream we usually eat. After freeze-drying, it is crumbly so the bits fall apart when you bite into it. The myth of astronaut ice cream might come from the press release of Apollo 7 mission. At that time, a company was under the contract to develop ice cream that can be stored at room temperature. They froze the ice cream and then used a vacuum pump to evaporate the ice under pressure. Air is retained inside the ice cream so that it is crunchy and can melt in the mouth instantly. Although the ice cream does not melt at room temperature, this astronaut ice cream has never been to space according to records. The space ice cream is not a real space food! With a freezer accompanying a space mission was launched in 2006, astronauts could eat real ice cream in space!

If you have a chance to go to space, what kind of food will you bring there? Being varied and diverse, do you know how space foods are made? Keep an eye out for our next post about space food!

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Space food in different countries
Image credit: NASA, JAXA

Published on 5 May 2021

Magnetar Flare in Nearby GalaxyBack to Top


NASA's Mars Odyssey spacecraft detected a powerful burst of X-rays and gamma rays on 15 April last year. Within 7 minutes, the burst reached the Wind satellite 1.5 million kilometres away from Earth, and reached Earth after 4.5 seconds. Several high-energy detection instruments including the Fermi Gamma-ray Space Telescope were triggered at almost the same time.

Since many instruments had detected this high-energy burst event, scientists could tell after studying that, the burst came from a spiral galaxy about 11 million light-years away, which can be considered as a close distance in the scale of the universe. Hence, It is believed that this burst was originated from a magnetar, rather than a usual gamma-ray burst. Otherwise, the signals will be much stronger than what have been detected.

Neutron stars are formed where some massive stars collapsed after the supernova explosion. Magnetar is a kind of neutron star with strong magnetic fields that is about 1,000 times stronger than an ordinary neutron star. Magnetars produce powerful flares that trigger gamma rays. This discovery helps astronomers to analyse the characteristics of the gamma rays from a magnetar, so as to distinguish the sources of different gamma-ray bursts in the universe.

More information:

Credit: NASA's Goddard Space Flight Center

Published on 3 May 2021

Space foodBack to Top


Unlike Earth, there are no supermarkets nor convenience stores in space. Astronauts need food to live on. Where does the astronaut's food come from? Is their food the same as what we eat? Astronauts don't eat space ice cream in space?

Space foods are brought to space from the Earth. Yuri Gagarin, the first astronaut up in space, took meat puree and chocolate sauce with him and ate in space. At that time, space foods were packed in a toothpaste-like tube. Astronauts squeezed out the paste-like food into their mouth. Nowadays, there are a multitude of space foods. They are almost indistinguishable from the food on Earth. Hamburgers and pizzas can be eaten in space.

Can all food be taken to space? No! The food that astronauts eat in space must meet stringent requirements, like being safe, delicious, nutritious, diversified, and compact. Space food needs to be well preserved and not easily deteriorated. Astronauts can safely consume them for several months. Also, it must meet the nutritional needs of astronauts (with balanced vitamins and minerals) without sacrificing taste and choices. Astronauts, like us, want to enjoy delicious and divergent food in space! Besides, the volume and mass of space food are important. Due to the high cost of each launch to space, it is necessary to reduce the payload of food.

What are some examples of space food? What kind of food cannot be taken into space? Are space foods different in different countries? Stay tuned for our next space food post!

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Space food
Image credit: NASA, JAXA

Published on 28 April 2021

Red wines that have been to SpaceBack to Top


To study the effects of the space environment on the ageing process of red wine, Space Cargo Unlimited selected 12 bottles of red wine from the year 2000 by Chateau Petrus and sent them to the International Space Station in November 2019. After staying in space for 438 days, these red wines were brought back to Earth by SpaceX Dragon spacecraft in January 2021.

Wine experts tasted the space wine. Experts said that the colour, aroma and taste of the space wine slightly differed from the Earth wine. Despite the same storage time (there is a slight difference between the two in relativity terms), experts thought the wine age of that of space was older than the ordinary wine. Some experts stated the space wine had a light brick red colour and with a hint of rose. The unopened space wines were sent for further analysis.

In addition to the bottle of wines, Space Cargo Unlimited also sent 300 grapevines to space in the same mission with aims to study the impact of space environment on plant growth. These vines will be analysed by biologists. Although the results have not yet been released, this experiment will help scientists to understand the growth of plants in different environments and cope with future climate changes or realise space farming.

Would you like to try the space wine? What kinds of food do you want to take to space and test how they differ from those on Earth?

Red wines that have been to Space
Image credit: Space Cargo Unlimited, NASA/Utah State University/Jessica Griffiths and The Standard

Red wines that have been to Space
Image credit: Space Cargo Unlimited, NASA/Utah State University/Jessica Griffiths and The Standard

Red wines that have been to Space
Image credit: Space Cargo Unlimited, NASA/Utah State University/Jessica Griffiths and The Standard

Published on 19 April 2021

Martian rainbow?!Back to Top


A rainbow on the Martian sky taken by the Mars rover Perseverance made the headline recently. NASA people explained that a natural rainbow is impossible on Mars because the Martian atmosphere is too dry and too cold for sufficient water droplets to stay. The "Martian rainbow" is actually a "lens flare" image artifact. There are more examples from the photos of the Apollo Moon landing missions.

Lens flare may be noticeable when there is stray light from strong light for example sunlight near the camera, that undergoes internal reflections inside the camera lens. Depending on the light source's position and the lens design, lens flares can show up as hazes, polygons or arcs in rainbow colors.

You think NASA's explanation is questionable? Flick your camera against light sources to create your original lens flares.

Martian rainbow?!

Martian rainbow?!

Martian rainbow?!

Martian rainbow?!

Published on 12 April 2021

NASA: Fly me on MarsBack to Top


Time flies! NASA's Perseverance rover has landed on Mars for almost two Earth months! Its partner – the Mars robotic helicopter Ingenuity has been released from the rover to the Martian surface. It is getting ready for its maiden flight around 11 April to demonstrate the technology of airborne scouting and prepare to explore other planets in the future.

If the flight is successful, Ingenuity will be the first man-made object that flies on planets other than the Earth. With a price tag of US$85 million, Ingenuity is charged and powered by solar energy and each flight can last for 90 seconds. The atmospheric pressure of Mars is very low: less than 1% of Earth's, which makes the flight a challenge to the engineers. So for the first flight, the helicopter will hover only a few feet up in the Martian air for around 20 to 30 seconds. After that, the team hopes to fly it higher and longer.

Perseverance is not idle too: it supports the flight operations, takes images, collects environmental data and connects the helicopter to the Earth's mission control.

Perseverance landed at Jezero Crater on 18 February 2021. It is NASA's cutting edge Mars rover for the "Mars 2020" mission. The mission will test oxygen production from the Martian atmosphere, collect and seal the Martian rock and soil samples.

Starting from 8 April, NASA will run a series of online briefings to cover the latest news on the helicopter's operations and findings. Please refer to the timetable here (mind the time zones):

To know more about the "Mars 2020" mission:

NASA: Fly me on Mars

NASA: Fly me on Mars

NASA: Fly me on Mars

Published on 9 April 2021

A new nebula discovered!Back to Top


NASA's Hubble Space Telescope team discovered a new nebula 2,100 light-years away from the Earth. What do you think it should be called?

The team actually did not discover a new nebula but revisited the Veil Nebula with a photo processed using new techniques. The Veil Nebula is the visible part of the Cygnus Loop (a supernova remnant in the constellation Cygnus), about 2,100 light-years from the Earth.

Notice the differences in the two photos? This reprocessed photo was taken by the Hubble's Wide Field Camera 3 through five different filters. The new technique highlighted the details of threads of ionised gases in the nebula (doubly ionised oxygen in blue; ionised hydrogen and ionised nitrogen in red), making the colour of the photo more vivid.

Nebula photos are always vibrant. Do you know that only some of the colours are real? Different elements in the nebula emit light in different colours after being excited, e.g. hydrogen emits red light, oxygen emits green light and sulfur emits blue light and photos that show the real colour of the elements are real-colour images. To the contrary, some elements in the nebula emit waves that are invisible to naked eye. Photographers use different wave-sensitive cameras to capture these wavelengths and add colours to facilitate viewing; scientists can also add different colours to indicate different elements, and these are false-colour images.

Post-production of photos are a piece of cake nowadays, everyone can be a photo post-production master with a phone in hand. Can we now see photos that are unprocessed? You can figure that out yourself!

Can you find the difference between the 2 photos?
Image credit: ESA/Hubble & NASA, Z, Levay

A new nebula discovered!
Image credit: ESA/Hubble & NASA, Z, Levay

Published on 1 April 2021

Wang Zhenyi – An Extraordinary Woman Astronomer from the Qing DynastyBack to Top

who believed in equality for both men and women, and women can also be heroesBack to Top


Do you have any female friends who are passionate about studying astronomy and stargazing (not those astrology or horoscope stuff)?

Whenever you talk about famous persons of science through the ages, it is most likely that you will come across a handful of names of male scientists. Nevertheless, there was a female in the Qing dynasty who has captured international attention because of her devotion to mathematics and astronomy. Her name is Wang Zhenyi (1768-1797), who was born during the reign of Qianlong more than two centuries ago. With the encouragement of her grandfather and father, Wang Zhenyi became an avid reader at an early age and loved reading so much that she frequently forgot to eat or sleep. While Wang Zhenyi was adept at literature and poetry, being no different to most ladies in China at that time, she also displayed an exceptional curiosity and affinity towards science. She was especially fascinated by the subject of astronomy, mathematics and cylindrical calculations. Thanks to the all-round education she received in her early years, Wang Zhenyi was also knowledgeable in geography and meteorology, and was herself a practitioner in Chinese medicine. During her short life spanning less than three decades, she wrote prolifically, especially on astronomy and mathematics. Unfortunately most of her works have been lost after her untimely death in 1797. The First Volume of the Pavilion of Virtuous Demeanor, which is still available today, collects some of her notable works on astronomy and mathematics. Amongst these are The Explanation of Lunar Eclipses (Yue Shi Jie), The Explanation of the Pythagorean Theorem and Trigonometry, Dispute of the Precessions of the Equinoxes and Theory of the Round Earth, among others. In The Explanation of Lunar Eclipses she used self-drawn diagrams to illustrate the principles of moon phases and eclipses.

one else I can turn to, I always feel disillusioned with the lack of progress…" Nevertheless, Wang Zhenyi still advocated women to educate themselves diligently, as all in all, women and men are of no difference in ability and intelligence. She believed that women could walk thousands of miles, could read thousands of books and with their knowledge women can also contribute to the society. Wang Zhenyi's devotion to science and her remarkable achievements won international acclaim and the International Astronomical Union named one of the craters of Venus after her in 1994 ( The well-known science journal Nature also featured Wang Zhenyi as one of the outstanding female scientists for a scientific research award that encourages young ladies to engage in research in science (, 00:19-00:36)。

On the International Women's Day, the Space Museum wishes every woman can shine in the area to which they are devoted.


Published on 8 March 2021

Announcement from spacecrafts: "The next station is: Mars"Back to Top


Did you remember the three spacecraft heading to Mars since mid-year last year? They are "Tianwen-1" of China, "Hope Probe" of the UAE and "Perseverance" of the USA. They had travelled more than 470 million km in 7 months in space. Now, they are about to arrive at their single destination!

Tianwen-1 has sent back its first image of Mars and is expected to land on the planet in May or June this year. Tianwen-1 is China's first Mars mission which aims to orbit and land on Mars to study the landscape, characteristics of the soil, atmosphere and magnetic fields, etc.

Hope Probe was successfully inserted into the Mars orbit on 9 February and was captured by the Martian gravity to orbit around the planet. Recently on Valentine's Day, scientists received the probe's first shot of the red planet. Hope Probe entered the space from Japan's Tanegashima Space Center in July last year. The probe will orbit Mars, study the dynamics of the Martian atmosphere and its interaction with space.

Perseverance are set to touch ground at the Jezero Crater on 19 February. There will be a live broadcast by NASA ( Perseverance's science objectives include: searching for any possible signs of ancient life; producing oxygen from the atmospheric carbon dioxide; collecting and storing samples of rocks and soil, etc. Moreover, the mission includes flying a robotic helicopter Ingenuity on Mars for the first time to demonstrate the technology of airborne scouting and to prepare for future explorations.

Stay tuned for the news from Mars during the Chinese New Year! Let's wish the spacecraft "good health" and success in their exploration!

Announcement from spacecrafts: "The next station is: Mars"
Image credit: Mohammed Bin Rashid Space Centre

More information:

Published on 18/2/2021

The Earth was spinning faster in 2020Back to Top


As the pandemic was raging, we may have wished the year 2020 to pass sooner. Actually, the rotation speed of Earth was faster than usual in 2020.

Since the record, the shortest day before 2020 was 5 July 2005. On that day, the time required for the Earth to spin once was 1.0516 milliseconds faster than the average. However, this record was broken 28 times in 2020. The shortest day was 19 July 2020, which was 1.4602 milliseconds faster than the average. As a whole, the year 2020 was the fastest one in the past 50 years.

In fact, the rotation speed of the Earth is affected by factors such as the atmospheric and oceanic activities at all time. Since the development of precise measurement technology, we know that the Earth's rotation speed is slowing down gradually. Therefore, scientists have introduced a leap second since 1972 so that the astronomical time, which is the time for the Earth to complete one rotation, would be consistent with the time of our clocks. However, the phenomena of Earth's decreasing rotation speed is reversing slowly. Some scientists estimate that the Earth will spin even faster in 2021. If the situation persists, we may have to use a negative leap second.

The Earth was spinning faster in 2020
Image credit: NASA

More information:

Published on 7/2/2021

Astronomers have found the most distant quasar known yetBack to Top


Our universe was born 13.8 billion years ago. All celestial objects we know were then formed one after another in the long river of time. Theoretically, massive compact objects would require a very long time to appear. Recently, astronomers have discovered a massive quasar that was formed only 670 million years after the birth of the universe.

A Quasar is a distant galaxy with a supermassive blackhole at its core. The super powerful accretion activity of the blackhole releases an extremely strong electromagnetic radiation, which can almost penetrate the entire universe. The newly discovered quasar is called J0313–1806. The supermassive blackhole at its core is about 1.6 billion times more massive than the Sun. In 2017, astronomers had found another blackhole that grew to 800 million times the mass of the Sun in the early universe. In addition to breaking the record, this new finding posts a great challenge for us to learn what kind of mechanism can be accounted for the formation of such a large object within a short period of time. This unsolved mystery would require more theoretical astronomers to answer for us.

Astronomers have found the most distant quasar known yet
Image credit: NOIRLab/NSF/AURA/J. da Silva

More information:

Published on 1/2/2021

The Dark Nebula under the Orion's BeltBack to Top


Not only is the constellation Orion easily recognisable, it also contains many deep-sky objects, and thus attracts amateur astrophotographers'cameras. This time, we will introduce to you a nebula with an interesting shape! Let's look at the dark nebula in this photo. What does it look like?

That's right. It's called the Horsehead Nebula. It is a dark nebula lying about 1,400 light years away and is made up of dark interstellar gases and dust. Normally, in order to see this kind of nebula, we need to rely on the light source behind it. The red glow of the emission nebula IC434 at the back of the Horsehead Nebula marks the shape of a horse's head for this dark nebula.

The Horsehead Nebula is located near Alnitak, one of the stars that represent the Orion's belt. However, the nebula is very dim, it can only be seen with an astronomical telescope. This photo is the first light image of the SPECULOOS Southern Observatory after its establishment. There are also numerous spectacular photos of this nebula which are taken by amateur astrophotographers around the world. Let's try to find them out on the internet.

The Dark Nebula under the Orion's Belt
Image credit: SPECULOOS Team/E. Jehin/ESO

Published on 24/1/2021

The frozen world beyond the EarthBack to Top


Cold waves had hit us one after the other that the temperature in Hong Kong dropped to 8.6°C on the 1/1, we had the coldest New Year's Day in 16 years and we haven't had experienced the cold weather for quite some time. If you look at the coldest East Antarctic Plateau on Earth, where the lowest temperature can reach -93.2°C, the temperature here is no big deal! Yet, the East Antarctic Plateau is not in the same league in the frozen world of the solar system, and is warm in comparison!

Where is the coldest place in the solar system? Right on our Moon! The poles of the Moon receive little sunlight and some areas can never have sunlight at all. In 2009, NASA's Lunar Reconnaissance Orbiter recorded the lowest temperature of -247°C while approaching the edge of the Hermite, a crater at the north pole of the Moon. Recently, studies have found that craters contain ice. So far, we haven't found other celestial body or part of the celestial body in the solar system with a lower temperature.

The second place comes to Neptune's moon - Triton. Triton has multiple icy volcanoes on its surface, which spew out nitrogen, dust and methane. As the average temperature of the Triton is as low as -235°C, the compounds in gaseous state on Earth freeze into solid instantly after eruption. These frozen compounds then fall back to Triton's surface. The third place comes to Pluto, which its average temperature is only 2°C higher than Triton. Pluto and Triton have similar surface composition but has more solid nitrogen than Triton. Can you see the heart-shaped area at the bottom right of Pluto? It's a vast plain of solid nitrogen!

The frozen world beyond the Earth

The Top 3 Coldest Places in Solar System

The Hermite Crater of Moon

Triton's Volcanic Plains

Published on 20/1/2021

Wonders of Jupiter from the Eyes of JunoBack to Top


What kinds of features would you think of when talking about Jupiter? Jupiter's atmosphere has various atmospheric phenomena, including some unstable bands, vortices, storms, and lightning. NASA launched a spacecraft called "Juno" to go to Jupiter in 2011. The spacecraft has been capturing images of Jupiter's atmosphere at a close distance since 2016 for us to peek into the wonder of Jupiter's atmosphere.

From the images taken by Juno, scientists found that Jupiter's atmospheric dynamics is far more complex than previously thought. You may check the latest close up images of Jupiter from the mission page of Juno. As the spacecraft is still operating normally, NASA announced in January 2021 to extend the mission of Juno to September 2025. Several famous Jovian satellites are included in Juno's new scope of observation to further investigate the entire system of Jupiter.

Wonders of Jupiter from the Eyes of Juno
Image credit: NASA/JPL-Caltech/SwRI/MSSS/Kevin M. Gill

Published on 18/1/2021

Going beyond Jupiter-Saturn Conjunction – Triple conjunctionBack to Top


The rare Jupiter-Saturn Conjunction last month was spectacular. How about THREE conjunctions in a year? Well, it is possible if Jupiter is in retrograde at the right moment!

What is a "retrograde motion"? The relative positions between the planets in the Solar System are constantly changing as they are travelling in distinct orbits around the Sun at different speeds. For most of the time we would see planets move from West to East against the stellar background on a daily basis ("prograde motion").

Going beyond Jupiter-Saturn Conjunction – Triple conjunction

However, they sometimes move in the opposite direction, from East to West ("retrograde motion", see Figure 1). (Let's try an experiment: identify some stuffs around you as foreground and background objects. Turn your phone's camera on and move it horizontally to observe the apparent changes of the objects' positions.)

Going beyond Jupiter-Saturn Conjunction – Triple conjunction

As illustrated in Figure 2, if Jupiter retrogrades right after a Jupiter-Saturn conjunction (happens about every 20 years), both planets will have two additional chances to "meet" (share the same ecliptic longitude or equatorial longitude, depending on the definition) within a year. We named these successive conjunctions as "triple conjunction" between Jupiter and Saturn. Moreover, triple conjunction can occur between other combinations of planet-planet (for example, Mars-Jupiter) or planet-star (for example, Mars-Spica).

Going beyond Jupiter-Saturn Conjunction – Triple conjunction

There is no Jupiter-Saturn triple conjunction between the 21st and 22nd centuries. The nearest occurrences are December 1980 to July 1981 and September 2238 to March 2239. How scarce this phenomenon is!

Published on 15/1/2021

Water Molecules on Sunlit Surface of the MoonBack to Top


The plot of exploiting resources in space is commonly seen in science fiction. In the future, it may not only be a fantasy as the Moon may become a potential target of space mining.

In the early 1960s, scientists had already proposed the possible presence of water ice on the Moon. As the lunar exploration programs of various countries have proceeded, more and more evidences for the presence of water molecules are found. At the end of last year, NASA discovered for the first time that water molecules can be found not only in the shadowed places, but also in the sunlit area of the Moon.

Stratospheric Observatory for Infrared Astronomy (SOFIA) has detected water molecules in Clavius Crater in the Moon's southern hemisphere by measuring the wavelength unique to water molecules. Despite the small amount, it is still a surprising result as the water molecules can survive under direct sunlight and without the protection from an atmosphere.

If the water on the Moon can be successfully exploited, not only can it be used as a supply for astronauts, but the hydrogen and oxygen in it can also be used as fuel for rockets. Therefore, the Moon may become a transit station for space exploration in the future.

Water Molecules on Sunlit Surface of the Moon
Image credit: NASA/Daniel Rutter

More information:

Published on 11/1/2021

Su Song and the Water-driven Astronomical Clock-towerBack to Top


The year 2020 marks the 1000th birth anniversary of Su Song, a famous astronomer of the Northern Song Dynasty. His most well-known technological achievement was the construction of the Water-driven Astronomical Clock-tower, which was one of the most outstanding astronomical instruments in ancient China.

Su Song was born in Tong'an County, Quanzhou Prefecture, which is now the Tong'an district in Xiamen, Fujian Province. At age of 70, he applied the most advanced knowledge in astronomy and technology in mechanical engineering at that time, to construct the Water-driven Astronomical Clock-tower that combined the functions of astronomical observation, celestial globes representation, time measurement and timekeeping.

The 12-meter-high Water-driven Astronomical Clock-tower was entirely driven by hydropower. At the top was the "armillary sphere" used for astronomical observation, it was able to track the Sun and stars through a power-transmitting system. The "celestial globe" at the middle recorded the features of the starry sky by the concept of a celestial sphere to demonstrate the movement of celestial bodies. A timekeeping system was installed at the bottom. The mechanism used inside the tower was similar to the escapement in modern clocks. Its marvellous design reveals the advancement in mechanical technology of the Song Dynasty.

After the completion of the Water-driven Astronomical Clock-tower, Su Song recorded the design and operation of the tower in his publication "Xin Yixiang Fayao". Unfortunately, the tower was destroyed after the "Jingkang Incident". The construction technology was lost for a long time as its descendants were not able to master the mechanical principle. The tower was reconstructed not until recent decades.

Su Song and the Water-driven Astronomical Clock-tower

Published on 28/12/2020

Jupiter-Saturn conjunction: When will they meet again?Back to Top


Observing and reading are lovely ways to learn astronomy, but doing some maths can be equally enjoyable.

"Jupiter-Saturn conjunction" in December involves Jupiter and Saturn, which have different orbital speeds. When they will meet again after the "goodbye kiss" in 2020? Let's find out by doing some simple calculations.

It takes Jupiter and Saturn approximately 12 and 30 Earth years to complete their orbits around the sun respectively. Planets' orbits are elliptical, but the orbits of Jupiter and Saturn have such a small eccentricity that they are more or less circular. Each year, Jupiter advances about 30° (360°/12) while Saturn about 12° (360°/30) along their orbits.

We want to know "when they will meet", we could think of "Jupiter pulling ahead of Saturn by 18° (30°-12°) in a year". Additionally, as they will meet again as soon as Jupiter completes a circle more than Saturn (i.e. 360°), the calculation becomes straightforward.

The answer of "When will they meet again?" is: 360°/18° = 20 Earth years later!

Jupiter-Saturn conjunction: When will they meet again?

Jupiter-Saturn conjunction: When will they meet again?

Jupiter-Saturn conjunction: When will they meet again?

Published on 19/12/2020

Getting closer and closer: Jupiter and Saturn (Part II)Back to Top


Five days left to the Jupiter-Saturn Conjunction on 21 December! Whenever you happen to glimpse at the SW sky at dusk, two bright stars that are slowly getting closer day by day should catch your attention. They are Jupiter and Saturn.

Although the Jupiter-Saturn Conjunction comes around every two decades, it is particularly special this time as the two planets, separated by a mere 0.1° or 6 arc min, will enjoy their closest encounter in the last 4 centuries. You may wonder how an angular distance of 1° in the sky looks like. Extend your hand to arm's length, your index finger-tip will be about 1° wide. You should now realise how small 0.1° really is! A casual look can be difficult to tell them apart, but if you observe them through telescopes, they could be visible in the same field of view.

The Jupiter-Saturn Conjunction this year also comes with a festive tinge because of its close proximity to Christmas. Actually astronomers through the ages have speculated that the "Star of Bethlehem" might actually be the Jupiter-Saturn Conjunction!

If you wish to witness this event, look for an open area and gaze upon the SW sky after sunset on 21st. The brighter Jupiter will show up first and when twilight sets in at around 6:30pm, you may see Saturn. Challenge yourself and try to tell them apart with your naked eyes. Make good use of your time to enjoy as the two planets will dip below the horizon after 8pm. We will livecast the Jupiter-Saturn Conjunction on our YouTube Channel ( and no registration needed. The link will be shared on that day. Please click on the link to join! Stay tuned!

The Change in Positions of Jupiter and Saturn in Hong Kong Night Sky

Handy Way to Measure Distances in the Sky

Published on 16/12/2020

Getting closer and closer: Jupiter and Saturn (Part I)Back to Top


The curator forecast the Jupiter-Saturn conjunction last week. The conjunction wouldn't happen until 21 December. Before that, you can witness their rendezvous. Visually, Jupiter and Saturn are separated by about 2 degrees (around four times the moon's size) today but are getting closer and closer to about 0.5 degree in two weeks. Before that, you have to recognise them first in the vast night sky.

Jupiter and Saturn are now in Sagittarius. Look low in the southwest sky before 8:30 pm, you can find a bright yellow star (apparent magnitude = -2) which is Jupiter. It can be easily observable even in the city as it is the brightest star in the area. Next to Jupiter you can find a dimmer Saturn (apparent magnitude = 0.6, still bright enough to see in the city) and in the east (or upper left) of Jupiter. With two bright stars so close together, it should be easy to find them!

The curator invites you to look for Jupiter and Saturn, take pictures, and check back day after day to see when they will "kiss" (but still separated by a very safe social distance of at least 730 million km). Will you accept this challenge?

Getting closer and closer: Jupiter and Saturn

Published on 2/12/2020

Astronomy Forecast for December 2020Back to Top


"Hello Everyone! The curator is bringing you the Astronomy Forecast…" Two exciting astronomical events are coming up in the last month of 2020!

From 4 to 17 December, the Geminid meteor shower is here again. In Hong Kong, the meteor shower peaks at around 2-3 a.m. of 14 December. Since the Moon will be very close to New Moon that night, moonlight will not be going to interfere with our observation of meteors. Given fine weather, if you go to a dark place with little light pollution, you can expect to see 20 to 30 meteors per hour. Among all the meteor showers of 2020, the Geminid meteor shower definitely boasts the best viewing conditions!

After the Geminid meteor shower, Jupiter and Saturn will have a celestial rendezvous known as the Jupiter-Saturn conjunction which occurs approximately every two decades. The two planets are now apparently getting closer to each other in the western night sky every day, and on 21 December, they will be so close that a casual look would find it difficult to tell them apart. This will be their closest encounter since the same event in July 1623. However, although Jupiter and Saturn look so close from our viewpoint on Earth, they are actually separated by about 730 million km, or 480 billion times the social distance of 1.5 m. So it is very safe for them to greet each other in the vast expanse of the Universe.

And that's all for now for the astronomy forecast. If weather permits, we will have live coverage for these two spectacular events on our YouTube Channel. Stay tuned!

Astronomy Forecast for December 2020

The Best Meteor Shower of the Year

The Closest Rendezvous of Jupiter and Saturn Over Four Centuries

Published on 27/11/2020

"Chang'e-5" is flying to the MoonBack to Top


The Long March 5 rocket blasted off at 4:30 am today (24 November 2020) from the Wenchang Space Launch Centre in China and took the "Chang'e-5" spacecraft to the Earth-moon transfer orbit. After landing on the lunar surface, Chang'e-5 will operate for about 2 days and attempt to bring around 2 kg of lunar soil samples back to the Earth. The samples would help scientists study the formation and evolution of the Moon. The last successful lunar sample return mission was the former Soviet Union's Luna 24 in 1976.

Chang'e-5 belongs to the "returning" phase of the Chinese Lunar Exploration Program, which consists of "orbiting", "landing" and "returning" phases. The "orbiting" and "landing" phases were completed in 2007 and 2013 respectively:

Orbiting: orbit the Moon (by Chang'e-1 and Chang'e-2)

Landing: land on the Moon (by Chang'e-3 and Chang'e-4)

Returning: return soil sample (by Chang'e-5)

Click the link to revisit the rocket launch:

Published on 24/11/2020

Jupiter and EuropaBack to Top


Storms on the surface of Jupiter have always been one of the major observation targets of astronomers. In addition to the famous Great Red Spot, there are also some smaller white spot storms.

This image of Jupiter was captured by the Hubble Space Telescope on August 25 this year, showing the recent charges in the atmosphere of this planet. The colour of the Red Spot Junior, which is seen under the Great Red Spot in the image, has been changing between red and white repeatedly for many years. It is turning from white to red now. In addition, a bright and stretched-out white spot can be seen in the northern hemisphere of Jupiter, which is a new storm in the making. Although it is common for this region to have one or more storms every six years or so, the Hubble Space Telescope has observed it in its early stage of evolution, showing the structure of disturbing airflow.

On the left of the image, you can also see one of Jupiter's moons, Europa. It is one of the few celestial objects in the solar system that might be able to find the signs of life.

Photo credit: NASA, ESA, STScI, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley) and the OPAL team

Jupiter and Europa
Image credit: NASA, ESA, STScI, A. Simon (Goddard Space Flight Center), and M.H. Wong (University of California, Berkeley) and the OPAL team

Published on 23/11/2020

A Beautiful Butterfly-like Planetary NebulaBack to Top


This picture shows a planetary nebula NGC 2899 taken by the European Southern Observatory's Very Large Telescope. This nebula is located in the constellation Vela. It looks like a butterfly flying in space, which is beautifully surrounded by the glowing clouds of hot gas.

Scientists believe that the appearance of NGC 2899 is related to its two central stars. One of the stars blew off its outer layers at the end of its life, and the other star interferes with the gas to form the nearly symmetric two-lobed shape. Among the many planetary nebulae, only 10-20% of them have such bipolar shape, which are some rare treasures in space!

A Beautiful Butterfly-like Planetary Nebula
Image credit: ESO

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Published on 16/11/2020

Omega CentauriBack to Top


This is an image released by European Southern Observatory showing the portrait of the globular cluster Omega Centauri.

Omega Centauri is the largest and brightest globular cluster in the sky. It is 16,000 light-years away from us and located in the constellation of Centaurus. This image has about 300,000 stars. However, within the region of its 150-light-year diameter, it is estimated that there are more than a few million stars. One interesting fact is that the stars in Omega Centauri have different ages and chemical properties where most other star clusters contain stars that are quite similar, which means Omega Centauri has a unique evolution process. Scientists think that Omega Centauri may be a remaining core of a dwarf galaxy stripped by our Milky Way.

Omega Centauri
Image credit: ESO/INAF-VST/OmegaCAM

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Published on 9/11/2020

Don't blink - International Space Station passing in front of the MoonBack to Top


The International Space Station (ISS) sometimes flies in front of the Sun and the Moon. I had successfully taken photos of the ISS transiting the Moon on the morning of October 12 this year in Kwun Tong, which only lasted ~0.3 seconds. The silhouette of the ISS can even be seen in the photo!

It is predicted that another ISS transit will occur at ~22:47 on November 5 (Thursday). At that time, people in parts of the New Territories West (such as Tsuen Wan, Kwai Chung and Tsing Yu), Cheung Chau, Lantau Island and Peng Chau will be able to observe it with binoculars at places with an unobstructed view in the direction of east-northeast. This transit will last about 1.9 seconds. You may find information on exactly when and where the transit will happen from

Please visit the Space Museum's Instagram for the video I took in October which shows the ISS pass and how quick it was. Don't blink or you will miss it!

ISS Transit

Published on 3/11/2020

Lord of the Rings - SaturnBack to Top


Saturn is indeed the "lord of the rings"!

This is a photo of Saturn taken by the Hubble Space Telescope on July 4, 2020. A distinctive ring system can be seen clearly. The rings of Saturn are mainly made of countless particles of water ice, with size ranging from micrometres to metres. If you take a closer look, you will find that the Saturn's ring is actually composed by several rings. There are some gaps between the rings. The most conspicuous one must be the "Cassini Division", separating the A and B rings. Can you find it in the photo?

Saturn's atmosphere is mainly hydrogen and helium with traces of ammonia, methane, water vapor, and hydrocarbons that give it a yellowish-brown appearance. The bands seen in the atmosphere are the result of strong winds in the upper atmosphere. Some of the bands change its colour occasionally.

Besides the rings, Saturn is also the "lord of the satellites". It is currently the planet with the most number of moons in the solar system. At least two of them are visible in this photo. Can you find them?


Published on 2/11/2020

Blue Moon that doesn't look BlueBack to Top


Following the Mid-Autumn Festival on 1st October, a full moon will occur again on the night of Halloween on 31st October! When there are two full moons in a single calendar month, the second one will be called the Blue Moon.

The meaning of the Blue Moon in astronomy was said to be originated from a book published in 1937. In 1946, an article in the magazine Sky & Telescope mistakenly defined the Blue Moon as the second full moon in a calendar month. As this magazine was popular, this misdefinition was widely spread and gradually become the current public understanding of Blue Moon. Blue Moon does not occur very frequently, but yet it doesn't mean our moon looks blue on the day.

There is an idiom "Once in a Blue Moon" to describe something that happens rarely. However, the appearance of the Blue Moon is actually not particularly uncommon. The lunar cycle lasts 29.5 days, so there will always be a full moon in each calendar month, which has 30 or 31 days, except for February. Therefore, as long as the first full moon occurs at the beginning of a month, the second one may appear again at the end of the same month. On average, a Blue Moon will appear every 30 months and the next one will come on 31st August, 2023.

But having that said, it will take 19 years to have the next full moon appearing on the Halloween night. If you don't want to miss the opportunity to see the Blue Moon on Halloween night, you might go outside or look out the window to find the round and big "Blue Moon" in bright white with the naked eye!

Blue moon

Published on 27/10/2020

Supernova Explosion Captured by the Hubble Space TelescopeBack to Top


We know that massive stars may experience a supernova explosion at the final stage of their evolution. This explosion is extremely violent, and the brightness produced may exceed the brightness of an entire galaxy. Apart from stellar evolution, supernova also appears in some binary star systems that contain a white dwarf. When a white dwarf exceeds the critical mass after absorbing a large amount of materials from its companion star, it will become a "Type Ia supernova".

Supernova explosions are almost unpredictable, but NASA has released a time-lapse movie recently, showing the evolution of a white dwarf into a supernova. The supernova 70-million light-years away is named SN 2018gv, and is located in the barred spiral galaxy NGC 2525 in the constellation Puppis. The Hubble Space Telescope began observing SN 2018gv in 2018, and spent about one year to take images of it continuously. In the time-lapse movie, we can see that its brightness had increased dramatically in a short period of time, reaching a peak at 5 billion times that of the Sun, and decreased slowly afterward.

Understanding the evolution of supernovae is very important to the development of astronomy and cosmology. Since the type Ia supernovae have the same origin, they have the same peak brightness too. Astronomers can use them to measure the distances between different galaxies and the Earth (for details, please search the keyword "standard candles"), and calculate the rate of the expansion of the universe to deduce the fate of our universe.

Supernova Explosion Capture
Photo credit: NASA, ESA, and A. Riess (STScI/JHU) and the SH0ES team

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Published on 26/10/2020

Sample Return Mission on Asteroid BennuBack to Top


After a four-year journey, NASA's explorer OSIRIS-REx will arrive at the asteroid "Bennu" on 20th Oct for sample collection. This is the second asteroid sample collection and return mission after the Japanese explorer Hayabusa. It is also the largest sample return mission from space since the Apollo program.

Since the surface of Bennu is covered with boulders, the explorer may be damaged if there is any mistake during the landing. Therefore, after months of works on analysing Bennu's terrain, NASA finally chose a rocky area named "Nightingale", located in Bennu's northern hemisphere, with a diameter of about 16 meters, as the sampling site. After arriving at the surface of the asteroid, the explorer will collect rocks and soil with the sampling arm immediately. The goal is to bring at least 60 grams of sample back to Earth. By analysing the samples, scientists could understand the features and resources of the early Solar System as well as the near-Earth environment.

After completion of the sample collection, the explorer will return to Earth in 2023. Let's look forward to the gifts that OSIRIS-REx will bring us!

explorer OSIRIS-REx
Photo credit: NASA/Goddard/University of Arizona

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Published on 19/10/2020

Black Hole Theory and ObservationTop


Three scientists from the UK, Germany and the USA, namely Roger Penrose, Reinhard Genzel and Andrea Ghez, have received the Nobel Prize in Physic this year for their outstanding contribution in the theoretical and observational studies on black holes.

In 1965, Roger Penrose used ingenious mathematical methods to prove that black holes are a direct consequence of Albert Einstein's general theory of relativity. He described black holes and the singularity at their heart where all the known laws of nature cease. Penrose and another famous scientist Stephen Hawking established the "Penrose-Hawking singularity theorems", which is a very important foundation on the research of black hole's singularity.

Reinhard Genzel and Andrea Ghez each lead a group of astronomers that, since the early 1990s, has focused on a region called "Sagittarius A*" at the centre of our galaxy. They found that the stars near that region are orbiting an invisible supermassive object. Their observational data match with each other, and estimate that there is about four million solar masses packed together in a region no larger than our solar system at the centre of the Milky Way galaxy, which should be a black hole as astronomers referred.

The Nobel Prize in Physics 2020 was divided, one half awarded to Roger Penrose, the other half jointly to Reinhard Genzel and Andrea Ghez.

Nobel Prize 2020 Black Hole Theory
Image credit: ESO/M. Kornmesser

Published on 12 October 2020

Explanation on the Mystery of Betelgeuse's DimmingTop


Betelgeuse, one of the brightest stars in the constellation Orion, began its dimming in October last year and reached its dimmest record in a century subsequently. A group of astronomers conducted an in-depth study about this phenomenon and published a research paper in August this year to explain the mystery of Betelgeuse's dimming.

The research team made use of the observational data on Betelgeuse in the past few years from the Hubble Space Telescope, including the analysis of its ultraviolet spectrum. They found that a large amount of hot material was moving from the surface of Betelgeuse to its outer atmosphere during September to November in 2019. The material finally left Betelgeuse, cooled down to form dust cloud and blocked some of the light emitted from Betelgeuse towards the Earth, causing the dimming effect we observed on the star.

Astronomers have long known that the brightness of Betelgeuse is always changing, but this unexpected dimming provoked speculation on whether Betelgeuse was about to experience a supernova explosion. The result of this study eliminated such speculation and revealed other stellar physics mechanism. Betelgeuse has already restored its expected brightness in April this year.

Explanation on Betelgeuse's Dimming
Image credit: NASA, ESA, and E. Wheatley (STScI)

Published on 5 October 2020

Reconstructing the Appearance of a Distant GalaxyTop


Can you guess what the halo in the image on the left is? Would it be an image of an annular solar eclipse? In fact, it is a galaxy called "SPT0418-47". The light from this galaxy has taken more than 12 billion years to reach Earth. You may have a question in your mind: Why can astronomers see celestial bodies so far away?

When there is another galaxy situated between a distant galaxy and the Earth, the divergent light emitted from the distant galaxy will be bent by the gravity of the foreground galaxy and directed to the Earth, so that we can receive a stronger signal. This effect is called the "Gravitational Lensing". Since SPT0418-47, the Earth and the foreground galaxy are almost aligned, SPT0418-47 appears as a near-perfect ring of light after being converged by the gravitational lensing. Astronomers used computer modelling to reconstruct its original appearance as shown in the top right image.

This study allows astronomers to acquire the information of the oldest galaxies in the Universe, and provides new clues to understand the evolution of galaxies as well as the Universe.

Reconstructing the Appearance of a Distant Galaxy
Image credit: ALMA (ESO/NAOJ/NRAO), Rizzo et al., ALMA (NRAO/ESO/NAOJ)/Luis Calcada (ESO)

Published on 28 September 2020

Close-up of Comet NEOWISE Top


Do you recognise the object in the photo? This is a close-up photo of comet C/2020 F3 (NEOWISE) that fascinated astronomy enthusiasts in July this year.

Astronomers had discovered this comet in March this year. It brightened to naked-eye level in late June and eventually became the brightest comet visible from the Northern Hemisphere since comet Hale-Bopp in 1997 in early July. Although comet NEOWISE has become difficult to observe from the ground since then, the Hubble Space Telescope took a photo of its core on August 8. At that time, the two were about 43 million kilometres apart. The image spanned about 18,000 kilometres across. However, the diameter of the comet's nucleus is estimated to be less than 4.8 kilometres across, even the Hubble Space Telescope was unable to see its surface.

In the photo, you can also see a pair of jets in opposite directions near the comet's nucleus, which is believed to be the gas and dust squeezed out from the sublimating ice on comet NEOWISE. It can be seen that comet NEOWISE remains intact after its closest approach to the Sun without breaking apart.

Image credit: NASA, ESA, A. Pagan (STScI) and Q. Zhang (Caltech)

Published on 21 September 2020

Relativity Bicycle Top


Cycling is a healthy exercise. As a speed lover, have you ever wondered what will happen if the speed of a bicycle approaches the speed of light, say 90% of the speed of light, which is about 970 million kilometres per hour?

Of course, in the real world, it is impossible to ride so fast. But scientists did use Einstein's theory of relativity to study the scenario of a "Relativity Bicycle" (a bicycle that travels almost as fast as light). Recently, British physicists, Evan Cryer-Jenkins and Paul Stevenson, have put forward some new insights about relativity bicycle and come up with the following scenario (ignoring the interaction between air molecules and the bicycle).

When the bicycle is speeding towards you, the light from the bicycle and the cyclist is blue-shifted to become invisible ultraviolet rays as a result of the Doppler effect. Being no longer visible, the bicycle and the cyclist appear in the surrounding landscape as a fast-approaching black silhouette. On the other hand, when the bicycle and the cyclist are moving away from you, the light is red-shifted to become invisible infrared rays. Once again they appear as a receding black silhouette and eventually disappear in the distance. The most intriguing thing happens at the instant the bicycle and the cyclist pass by your side when light shifts from blue to red, a blast of pulsating rainbow tones will suddenly burst out!

If you want to know more, you can refer to this paper:

Finally, as a friendly reminder from the editor, please ride at a safe speed.

Published on 18 September 2020

Sign of Life in the Atmosphere of VenusTop


Scientists have discovered a small amount of phosphine in Venus's atmosphere. Since this compound can be produced by microorganisms, and there is no other mechanism entitled for the production of this amount of phosphine, scientists are speculating that microorganisms may exist on the planet Venus.

Phosphine is made up of one atom of phosphorus and three atoms of hydrogen. It is a toxic gas for larger organisms, but can be released by microorganisms. Phosphine can be found on Earth, Jupiter and Saturn. However, for other rocky planet like Venus, the production mechanism of this compound is very limited. By observing a selected millimeter wave from Venus's atmosphere using the JCMT telescope in Hawai?i and ALMA telescope in Chile, scientists discovered a phosphine absorption line which implies the existence of phosphine in Venus's atmosphere.

The concentration of phosphine found on Venus this time is estimated at about 20 ppb, which means there are twenty phosphine molecules in every billion. Although the amount of molecules is so tiny, no other known mechanisms including sunlight, volcanoes, or lightning, are able to account for it. If there are no other unknown chemical reactions, the only remaining choice would be some living microorganisms. What do you think?

20200915 Venus
Image credit: ESO/M. Kornmesser/L. Calcada

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Published on 15 October 2020

Westerlund 2 and Gum 29Top


This image was taken by the Hubble Space Telescope in near-infrared light. A star cluster composed of thousands of stars can be seen on the right side, known as Westerlund 2. There is a colourful nebula next to it called Gum 29.

Gum 29 is located 20,000 light-years away from us in the constellation Carina. It is an active star-forming region with rich colours and plenty of pillars gases. Westerlund 2 contains numerous hot, bright, and massive young stars. The stars are unleashing torrents of stellar winds that push the molecules in Gum 29 outward, forming a huge cavity around the star cluster. The blue stars seen throughout the image are stars closer to us in the Milky Way galaxy not associated with Westerlund 2 or Gum 29.

20200914 Westerlund 2 and Gum 29
Image credit:: NASA, ESA, the Hubble Heritage Team (STScI/AURA), A. Nota (ESA/STScI), and the Westerlund 2 Science Team

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Published on 14 October 2020

The Response of Mammalian Immune System to the Imaginary Space GermTop


Humans have been working tirelessly to search for extraterrestrial life. Scientists believe liquid water may exist in more than one celestial body in the solar system. They also found amino acids, one of the basic building blocks of life, in meteorites from time to time. The existence of extraterrestrial microorganisms seems possible. In the future, if an astronaut travel to other celestial bodies, and even bring the collected rocks back to Earth, then it is possible to make contact with the extraterrestrial microorganisms composed of special amino acids. If these microorganisms are ingressive, can the human immune system respond effectively against them?

Scientists used mice as a test subject to examine the responses of mammalian immune systems to the peptides composed of two amino acids commonly found on meteorites. It was found that when mouse T cells, which are crucial to the immune responses, were exposed to the peptides, the activation level was only 15% and 61%, which was less efficient compared with their responses to peptides composed of common amino acids on Earth. This means that when humans come into contact with extraterrestrial microorganisms, the immune system may not be able to respond effectively, increasing the potential risks of space exploration missions.

20200902 Mars Rover Perseverance
Photo credit: NASA/JPL-Caltech

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Published on 7 September 2020



When I was still a junior secondary student, I was tricked by a senior. She asked me: Could you jump over your own shadow? My first thought – it was all about length. I could definitely jump over my own shadow when it is short. So, I tried to find out when the length of my shadow would be the shortest. I went to the rooftop at different times and recorded the length of my shadow. I got what I wanted – it was the shortest at noon when the sun was right above me.

After this, my focus gradually shifted from jumping over the shadow to studying the relationship between the length of the shadow and time. Later, I also noticed the length of the shadow varied with different months in a year, even if the measurement was taken at the same moment in a day. The shadow in summer is always shorter than it is in winter.

This scientific principle is exactly the theoretical base of an ancient astronomical instrument called the Gnomon. The ancient Chinese used this device to define the 24 solar terms. Farmers in the past used the 24 solar terms to determine sowing and harvesting times. That's why I say Gnomon is an astronomical instrument that can influence food production!

Let's think
In Hong Kong, every year there are two days that everything casts no shadow at around noon time. This phenomenon called "Lahaina Noon", do you know why this happens?

20200902 Gnomon

Published on 2 September 2020

Armillary Sphere (Part 2)Top


As mentioned in the last episode, ancient Chinese astronomers used the Armillary Sphere to measure the position of celestial bodies.

To use the Armillary Sphere, we need to understand the concept of the 28 mansions in ancient Chinese astronomy. The 28 mansions were used as reference points by ancient Chinese to describe the position of celestial bodies. Their names were carved on a certain ring of the Armillary Sphere.

In the Armillary Sphere there are three sets of rings: The outermost set is called the Ring of the Six Cardinal Points (Liuheyi), the middle one is the Ring of the Three Stellar Objects (Sanchenyi) and the innermost the Ring of the Four Movements (Siyouyi). This set comprises the Hour-angle Circle, Celestial Axis and a Sighting Tube. Embodying different astronomical concepts like the 28 mansions, the celestial equator, the ecliptic and the 24 solar terms, some of these rings are fixed while some are movable and can be turned manually.

Doing your head in? Don't worry! Let's just leave the complex structure of the Armillary Sphere aside. Next time when you visit the Astropark, do not forget to take a selfie with the Armillary Sphere. It is an exquisite piece of artwork that blends astronomy with art. Take a look at its features and learn about the astronomy behind it. It is also an excellent opportunity for us to appreciate the wisdom of our ancestors.

Let's think
1. How many circles are there in the Armillary Sphere?
2. The circles that can be turned in the Armillary Sphere share the same rotating axis. At which direction does this axis point?

20200826 Armillary Sphere

Published on 26 August 2020

Chinese Valentine's Day, when Altair and Vega meetTop


The 7th day of the 7th month of the Lunar Calendar is known as the Qixi or Tanabata in Japanese. In Chinese mythology, Altair and Vega reunite on this day. The weaver girl was the granddaughter of the Jade Emperor and had weaved many colourful clouds in the sky and was in love with the cowherd but were separated by the Heavenly Mother with the Milky Way. In extreme grief the Jade Emperor allowed them to cross the Milky Way with the magpie bridge and met each other during the Qixi every year.

Altair (the star of cowherd) is 16 light-years away from Vega (the star of weaver), so they can't get together in one day. However, the day of 7th of the 7th lunar month has become a festival in some places with different celebrations like having fried dumplings and letting off fireworks, or even treat this day as the Valentine's Day. In Hong Kong, we don't celebrate the day as in other places, but we can still get to know Altair and Vega through stargazing.

Altair is the brightest star in the constellation Aquila and the twelfth brightest star in the sky whilst Vega is the brightest star in the constellation Lyra and the fifth brightest star overall. If you look carefully, you will find another bright star nearby forming a triangle with Altair and Vega. This is Deneb of the constellation Cygnus. These three noticeable stars in the summer sky are known as the summer triangle. When the sky and weather is clear, we can observe them easily with our naked eyes even in the city! Wish you all can enjoy the glimpse of starlight on this romantic Chinese Valentine's Day with your friends and families!

20200825 Summer Triangle

Published on 25 August 2020

Photographing a Multi-planetary System 300 Light-years AwayTop


We believe planets are quite common in the universe, but only a few of them were observed directly. Recently, astronomers have successfully photographed two planets near a sun-like star for the first time.

This star, numbered TYC 8998-760-1, is about 300 light-years away from the Earth. It is very similar to the Sun in terms of size and mass. The two planets orbiting the star are called TYC 8998-760-1 b and TYC 8998-760-1 c respectively. They are about 160 and 320 astronomical units (one astronomical unit is about the average distance between the Earth and the Sun) apart from the host star, and their masses are 14 and 6 times larger than that of Jupiter.

By using the European Southern Observatory's Very Large Telescope, astronomers first blocked the strong light from the star with a device called coronagraph, then photographed the dim planets next to it. The telescope was capturing an infrared waveband as the hot and young planets appear brighter in infrared light. This method may help to observe more exoplanets, thus allowing us to know more about the formation and evolution of the solar system itself.

More information:

20200824 Photographing a Multi-planetary System 300 Light-years Away
Photo credit: ESO/Bohn et al.

Published on 24 August 2020

Armillary Sphere (Part 1)Top


How fortunate we are! If we had lived in the ancient times, we could only have taken a sneak peek at this astronomical instrument.

You may ask, "It's just an instrument, not some secret weapon; why the big fuss if people in ancient times wanted to lay their hands on it? The reason is, studying anything related to the sky in private was strictly prohibited among the general populace in ancient China (you might end up in stockade if you did so!). Ancient Chinese believed that the starry sky was a reflection of the secular world. Different celestial phenomena, including the motion of the Sun, Moon and planets, could be viewed as portents of the rise and fall of regimes. As this instrument was used to measure the positions of celestial bodies, it could, to a certain extent, reveal some divine prophecies including such heavily guarded secrets like the well-being of the supreme ruler. It therefore comes no surprise that the study of astronomy was taboo in ancient China.

Astronomy in ancient China thus followed its own distinct path of development. It began with astrological purposes in mind but serendipitously stimulated the development of observational instruments and the comprehensive documentation of astronomical phenomena. Known as the Armillary Sphere, this instrument is made of three sets of giant rings. The hollow tube in the innermost ring, called the Sighting Tube, is used to point at the target of observation. For example, when we want to observe Mars, we will adjust the Sighting Tube until we can see it through the Tube. The position of the planet can then be read from the graduations on the Armillary Sphere. You may wonder, "Really that simple? Isn't it similar to a child's play of rolling a paper tube to mimic a telescope?

When looking closer at the device, we could also see that there are markings on some of the giant rings. What are these rings for? We will answer these questions in the next episode. Stay tuned.

Let's think
1. What features on the Armillary Sphere show that it is a royal instrument that can only be used by the imperial court?
2. A country has an icon of an Armillary Sphere on its national flag. Which country is it? What is so special about Armillary Spheres in the history of this country?

20200819 Armillary Sphere

Published on 19 August 2020

Towards Mars! Top


China, Emirates, and the United States launched three probes to Mars not long ago respectively. Have you ever wondered why multiple countries launched the Mars probes within a short period of time? Was it a coincidence or a deliberate arrangement?

In fact, July to August this year is the "Launch Window" to reach Mars. Any Probe launched at this period can arrive at Mars with the highest efficiency through the "Hohmann Transfer Orbit". Firstly, the probe orbits around the Sun along with the Earth in a nearly circular orbit. As it launched, the probe accelerates and enters an elliptical orbit, whose aphelion (the position of the orbit farthest from the Sun) is at the distance of Mars' orbit. If a suitable launch window is chosen, the probe will meet Mars when it arrives at the aphelion of its elliptical orbit. At this time, the probe will accelerate again to transfer its elliptical orbit into the orbit of Mars. It can then reach the destination by being captured by the planet's gravity.

This kind of transfer obit is not the fastest or shortest, but it is very fuel-efficient. Hence, it is utilised in missions like planet exploration and satellite orbit transfer. The launch window to Mars opens once per about two years, various countries would grasp this opportunity to go to Mars together.

20200817 Hohmann Transfer Orbit

Published on 17 August 2020

The Giant Petulant Star – Eta Carinae Top


This magnificent picture was taken by the Hubble Space Telescope under ultraviolet light. The object is a star named "Eta Carinae", which is about 7,500 light-years away from the Earth. It is one of the most massive and brightest known stars. However, it doesn't look like a star in any way, right? This giant star is actually very unstable and has a history of eruptions. Scientists believe that this giant star will present a supernova explosion in the short future (at least thousands of years since now) ...

Although Eta Carinae is relatively close to the Earth, scientists estimate that this supernova explosion in the future will not create a substantial impact on the Earth. At that time, there may just be an extremely bright star displayed in the sky!

More information:

20200811 Eta Carinae
Photo credit: NASA, ESA, N. Smith (University of Arizona), and J. Morse (BoldlyGo Institute)

Published on 10 August 2020

A Trio of Missions to MarsTop


Successfully launched into space in end of July, the US's Perseverance is now speeding at more than 50,000km/h towards the red planet. As one of the pioneers of Solar System exploration, the US had a head start and scored early success in the first successful fly-by of Mars (Mariner 4) as early as the 1960s. However, two newcomers have also joined US in this year's launch window to Mars. They are the United Arab Emirates' Hope and China's Tianwen-1.

All three missions are quite distinct and unique in their own right in terms of mission approach and objectives. The UAE chose to send a probe to Mars, which is currently 100 million km away, as its first space mission ever conducted. One special feature of this mission is its high degree of international participation. The Hope probe was jointly developed by the UAE with several American universities. Its journey to Mars began with a blast-off atop a Japanese rocket at the Tanegashima Space Center in Japan. Right now, it is utilising NASA's Deep Space Network to transmit data and signal back to Earth. Through occupying a unique orbit never taken by other probes before, the Hope probe will collect data at different altitudes of the Martian atmosphere through various seasons of the year. It will help scientists better understand the evolution of Mars, shedding light on what makes its atmosphere thin out and eventually dominated by carbon dioxide, and why liquid water no longer exists on the planet surface.

China commenced its first Mars exploration mission by launching Tianwen-1 on 23 July with the blast-off of the Long March-5 Y4 carrier rocket. Tianwen-1 aims to complete "orbiting, landing and roving" in this mission. One of the major tasks of Tianwen-1 is to fathom the possibility of life on Mars through radar to search for pockets of subsurface water. A research team from Hong Kong has also contributed to this challenging mission. Led by Professor YUNG Kai-leung of The Hong Kong Polytechnic University, the team developed the "Mars Landing Surveillance Camera" with CAST. Mounted on the lander, it will be used for collecting data to monitor the landing status. The information is critical for the successful movement of the rover across the Martian surface.

Launch into space is only the first step. The three Martian probes are scheduled to arrive at Mars in February 2021. We anticipate these missions would bring about knowledge and experience that are precious to our future exploration of the Solar System. Through these missions we can learn more about planetary evolution, the origin of life and the possibility of future human migration to other planets.

20200805 Hope Probe
Image credit: Mohammed Bin Rashid Space Centre

Published on 4 August 2020

Two exoplanets closest to the Earth foundTop


Proxima Centauri is about 4.2 light-years away from the Earth and is the closest star to us besides the Sun. Astronomers claimed to have discovered a planet in Proxima Centauri in 2016 with an orbital period of about 11 days called "Proxima Centauri b". This discovery was finally confirmed at the end of May this year, making Proxima Centauri b the closest known exoplanet.

Just a few days after the confirmation of Proxima Centauri b, astronomers announced there is another planet orbiting Proxima Centauri. In early 2020, astronomers had already wondered the existence of a planet with an orbital period of more than 5 years around Proxima Centauri. Later, another group of astronomers reviewed some data collected by the Hubble Space Telescope over the past 25 years and confirmed that there is a planet revolving around Proxima Centauri with an orbital period of 1,907 days, and hence named it as "Proxima Centauri c".

Being the closest exoplanets to the Earth, we do want to know if aliens exist or not. Preliminary speaking, among thousands of known exoplanets, both Proxima Centauri b and Proxima Centauri c are not a candidate for being habitable. However, these discoveries tell us, the number of planets outside the solar system is not a few, maybe we can find a planet like the Earth not far away (is 4 light-years far?). Let's wait and see!

20200803 Artist's impression of the planet orbiting Proxima Centauri
Image credit: ESO/M. Kornmesser

More information:

Published on 3 August 2020

The Very Different Near and Far Sides of the MoonTop


Have you ever heard of the legend about a rabbit living on the Moon? Now we know it is just people's fantasy based on the distinct gray regions (called the lunar maria) on the lunar surface facing the Earth, which looks like a rabbit pounding medicine.

Since the rotation period and the orbital period of the Moon are the same, the Moon always keeps the same face pointing towards the Earth, and its far side remained unobserved until it was first photographed in 1959 by the spacecraft Luna 3. Scientists found that there are almost no lunar maria on the far side of the Moon. The reason why the two sides of the Moon are so different has been a hot research topic among scientists. New research papers about this topic can be seen from time to time.

Recently, a new idea is suggested by a research team. The asymmetry of the lunar maria could be due to an uneven distribution of radioactive elements on the lunar surface at the time when the Moon formed. Some areas on the near side of the moon are heated up by the radioactive activity, producing an active volcanic activity and leaving the sign of lunar maria.

20200720 Near and Far Sides of the Moon
Photo credit: NASA/Goddard/Arizona State University

Published on: 27 July 2020

Monster Black Hole in the Early UniverseTop


Many black holes are formed after supernova explosions, but there are also many exceptions, such as supermassive black holes. Astronomers speculate that supermassive black holes exist in the quasars of the early universe, but the formation mechanism is still unknown.

Recently, astronomers discovered a quasar which has existed since 13 billion years ago. It is the second farthest quasar known and has a monster black hole with 1.5 billion times the mass of the Sun. The mass of this supermassive black hole is at least 2 times bigger than that in another known quasar further away. To achieve the current mass, it had to have at least 10,000 times the mass of the Sun within about 100 million years since the birth of the universe.

How can such a supermassive celestial object form within a short period of time? Astronomers have different thoughts, one of which states the supermassive black holes are the result of a series of chain reactions. Nascent black holes radiate energy during accretion and heat up gas clouds nearby to make them collapse more easily. It ends up increasing the mass of the black holes, so that more energy is radiated and the same process repeats. However, a convincing theory is not yet available. The newly discovered quasar is thus a great challenge to our understanding on the origin of supermassive black holes, formation of galaxies, and the evolution of the universe.

20200720 Monster Black Hole in the Early Universe
Photo credit: International Gemini Observatory/NOIRLab/NSF/AURA/P. Marenfeld.

Published on: 20 July 2020

The Smell of SpaceTop


There is no air in the space and have you thought of how it would smell like?

Space is a vacuum and no astronauts could have ever smelled it in the traditional sense, but they have smelled it indirectly. When astronauts are working outside the International Space Station, the smell of space adheres to their spacesuits, and they then carry the distinct odor back into the station. NASA Scientist, Louis Allamandola explained that the odor-causing spaceborne organic compound are found in coal, oil and even barbecue. No wonder some astronauts have described the smell of space as the seared steak!

In order to help astronauts get used to the space environment before launch into orbit, NASA and chemists developed a scent mimicking the smell of space decades ago. Recently, a team in the US manufactures a perfume to bring this smell back down to Earth according to the recipe released by NASA for astronauts' training. They hope to donate the perfumes to local kindergartens, primary and secondary school for the STEM education through senses. The approaches to learn about the space keep emerging as the mindblowing discoveries of the universe. So, could you imagine the next milestone in space exploration?

20200716 Astronaut on Spacewalk
Photo credit: NASA

20200716 Space perfume
Photo credit: au de Space

Published on 16 July 2020

Opposition of Jupiter Staged in MidsummerTop


Summer is a good season for stargazing as the visibility of the sky is generally high. You may pay attention to the astronomical phenomenon "Opposition of Jupiter" which will take place on July 14, 2020. When the planet Jupiter arrives at a position almost in line with the Earth and the Sun, opposition of Jupiter occurs. At this time, we can see a very bright Jupiter since it is relatively close to the Earth. It is also the best time to take images of this planet.

Jupiter is located at the east of the constellation Sagittarius and has a star magnitude of -2.7. We can find her near the eastern horizon at 7:30 pm, and the planet remains visible throughout the night. If you have a pair of binoculars or an astronomical telescope, you may see several satellites near Jupiter, and even the atmospheric bands on her surface.

Moreover, the bright Saturn of star magnitude 0 can be found next to Jupiter. Both of them are so bright, which can be found very easily. Some other celestial objects such as Mars, Venus and even Mercury can also be seen after midnight and before sunrise. It would be a good time to watch the planet family of the solar system!

20200713 Opposition of Jupiter

Published on: 13 July 2020

The Moment When Things Cast No Shadow Top


The image compares the situations of a rocket model under the sunlight at noon and afternoon in a recent day. Have you noticed something strange? Yes, the rocket model at noon seems not casting any shadow. Under most circumstances, even at noon, objects on ground that exposed to sunlight will cast long shadows, but there is an exception to this well-known phenomenon, which is the time when "Lahaina Noon" occurs during every summer.

In addition to the motion from the east to the west, the sun also moves in the south-north direction slowly. During summer solstice, the sun reaches the overhead position of any region on the Tropic of Cancer (23.5°N). Since Hong Kong is located at 22.3°N, the sun passes through the zenith of Hong Kong before and after the summer solstice. When it happens, the sun shines directly overhead, Lahaina Noon occurs. If some bamboo poles or other objects are erected outside at this particular time, their shadows will simply disappear.

This year, Lahaina Noon occurs at 12:22 p.m. on June 3 and 12:29 p.m. on July 9 respectively in Hong Kong. You may pay attention to the street on Thursday at noon to check if the shadows of objects are slowly shrinking and disappearing.

20200707 The Moment When Things Cast No Shadow

Published on: 7 July 2020

The Curious Case of a Disappearing ExoplanetTop


In 2004, the Hubble Space Telescope spotted presumably a bright exoplanet near the star "Fomalhaut" just 25 light-years away, known as "Fomalhaut b". However, astronomers found that, from the observational data in the following years, this exoplanet is fading gradually.

Summarising the observation data from many years, astronomers think that Fomalhaut b may not be a planet. The bright spot observed by the Hubble Space Telescope might be the result of a collision of two stellar objects after all. As the debris of the stellar objects left behind after this collision slowly dispersed, the brightness of the bright spot also dropped gradually.

Aside from the decrease in brightness, the movement of Fomalhaut b did not conform to a normal planetary orbit but an escape trajectory of a group of stardust affected by its host star. This unusual trajectory also suggested what Hubble Space Telescope witnessed was a collision instead of an exoplanet.

Although it might be a little disappointing to learn that Fomalhaut b was not an exoplanet, to witness a collision between two stellar objects with the Hubble Telescope is quite a rare occasion.

20200629_Disappearing Exoplanet
Photo credit: NASA, ESA and A. Gaspar and G. Rieke (University of Arizona)

More information:…/news-2020-09

Published on: 29 June 2020

Astronomers discover the closest black hole to EarthTop


Black holes are celestial objects that do not emit any electromagnetic wave and therefore we cannot observe them with the naked eye alone. Astronomers usually identify the existence of black holes by detecting X-rays emitted by the accretion disk near them. Not long ago, during a study of a binary star system designated as HR 6819, astronomers discovered that one of the stars in the binary system orbits an unknown celestial object at a period of 40 days, and calculated that the mass of this unknown celestial object is at least 5 times that of the Sun. Hence, it is concluded that this celestial object should be a black hole and HR 6819 should be a triple star system.

HR 6819 is 1000 light years away from the Earth. Located in the constellation Telescopium at the southern celestial sphere, it has an apparent magnitude of 5.3 which is visible to the naked eye. Before this study, the closest known black hole to Earth was about 3000 light years away. This discovery has rewritten the record and marks the first black hole that can be located by naked-eye observation.

Closest Black Hole
Photo credit: ESO/L. Calcada; ESO, IAU and Sky & Telescope

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Published on: 16 June 2020

The Stunning Nebula Image "Cosmic Reef"Top


To celebrate 30 years since the launch of the Hubble Space Telescope, NASA released a stunning image taken by Hubble, showing the giant red nebula NGC 2014 and its blue neighbour NGC 2020.

These two nebulae are part of the Large Magellanic Cloud located at more than 160,000 light years away from the Earth. On the right of the photo, the NGC 2014 is an active region of star formation. The strong radiation of new born stars cause the excitation of hydrogen atoms and the corresponding emission of red light. On the lower left of the photo, the NGC 2020 was originated from the birth of a massive star, the radiation of the star created a cavity and ionized the surrounding oxygen atoms to produce blue light. This image is nicknamed the "Cosmic Reef" because of the coral reef-like appearance.

So far, the Hubble Space Telescope has accomplished 1.4 million observations. It is going to stay operational in the next few years to provide more data for astronomical research and capture beautiful images of the space just as the "Cosmic Reef".

Cosmic Reef
Photo credit: NASA, ESA and STScI

Published on: 9 June 2020

Exoplanet similar in size and temperature to Earth Top


NASA retired the Kepler space telescope in November 2018, but astronomers are still analyzing the data obtained from it. Recently, astronomers found an exoplanet hidden in the dataset captured by the telescope during 2010-2013. This planet is called Kepler-1649c, turned out to be one of the most Earth-like exoplanets in size and temperature found in the Kepler project.

Kepler-1649c is a rocky planet located 300 light-years from Earth. It is about 1.06 times larger than the Earth and receives 75% of the amount of light from its star as the Earth does from our Sun. Moreover, it is sitting right in the habitable zone of its system, in which the temperature is just right for liquid water to exist on the planet. However, Kepler-1649c is orbiting a red dwarf star (Kepler-1649). This type of star has very active solar flares that would make any potential life of Kepler-1649c very challenging. At this stage, it would not be able to tell if there is any possible alien life on Kepler-1649c.

The Kepler space telescope is dedicated to finding exoplanets using the transit method. As it had obtained a huge amount of data, astronomers used an algorithm to identify "false positives" signals. A group of astronomers are taking a second look at all the processed data to weed out any mislabelled data. Kepler-1649c is a planet that got misidentified before.

Earth and Kepler1659c
Image credit: NASA/Ames Research Center/Daniel Rutter
(The Kepler-1649c in the image is an artist's impression.)

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Published on 3 June 2020

The Most Anticipated Comet of the Year?Top


Astronomers discovered a comet called C/2019 Y4 in December last year, and had predicted that it would become very bright this summer. Hence, this comet was once hailed as the most anticipated comet in 2020.

What's surprising is that C/2019 Y4 had brightened gradually before the end of March, but then its brightness started to decrease in April. As seen from the images taken by the Hubble Space Telescope on 20 April and 23 April, the comet has broken apart on its journey to the Sun. Although some experts found that the comet has become brighter again in May, it is still unknown whether it can recover from death.

While C/2019 Y4 may disappoint many astronomy enthusiasts, another comet C/2020 F8 (SWAN), which was discovered in March this year, is getting brighter gradually that it is visible to the naked eye. However, as it is too close to the Sun, normal citizen may not be able to observe it, but we can still enjoy the beautiful photos taken by professional astrophotographers.

C/2020 F8(SWAN)
Photo Credit: Luc Perrot

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Published on 25 May 2020

A Dance between the star S2 and the Black HoleTop


A star named "S2" dancing around the supermassive black hole at the centre of our Milky Way Galaxy has been observed by the "Very Large Telescope" of The European Southern Observatory. It has demonstrated that the prediction made by Einstein's general theory of relativity still holds true even in the most extreme environment.

Gathering the data from 27 years of observations, astronomers have shown that S2's ellipse-shaped orbit does not stay fixed in space. The orbit of S2 shifts around like drawing a rosette - a phenomenon known as Schwarzschild precession.

In fact, the Schwarzschild precession was first observed in our Solar System. Over a century ago, astronomers had already known that the planet Mercury behaves like S2 does, but they could not explain it with any physics theories at that time. In 1915, Einstein successfully explained the weirdness of Mercury's motion with his general theory of relativity, and it became an important evidence in favour of his new theory.

Since S2's orbit follows general relativity so well, astronomers hope that it can help us unlock more secrets about the formation and evolution of supermassive black holes. This dance between S2 and the black hole is really important!

 star S2 and the Black Hole
Photo credit: ESO/L. Calcada

Published on 13 May 2020

Saturn's Mysterious Heat SourceTop


The solar system has many unsolved mysteries, including the abnormally high temperature on the atmospheric surface of the gas giants. It seems that they are heated by a hot source other than the Sun. The mysterious heat source has been a hot discussion topic for astronomers.

Exploring Saturn for 13 years, the Cassini spacecraft crashed into Saturn's atmosphere in 2017, but it still collected data of Saturn's atmosphere during its last orbit to reveal the secret of the mysterious heat source. It was found that Saturn's atmosphere has the highest temperature near the poles, which are the places where Saturn's auroras appear. Astronomers believe that, Saturn's auroras and the induced electric currents heat its upper atmosphere, and the heat is carried to other area by the strong air flow, which accounts for the high temperature of Saturn's atmosphere.

By understanding more about the reaction between the solar wind and the gas giants, scientists could resolve the mystery so called "energy crisis" in the solar system and understand more about the exoplanets in the universe.

Image credit: ESA/Hubble, NASA, A. Simon (GSFC) and the OPAL Team, J. DePasquale (STScI), L. Lamy (Observatoire de Paris)

Published on 5 May 2020

Working remotely from 225 million km away?Top


Recently, working from home is the norm around the world. To maintain social distance, organisations requiring employees to work from home are the usual practice now. With no exception, NASA implements the measures to their mission teams, including the Curiosity Mars rover mission team.

The Curiosity Mars rover mission team is based in the Jet Propulsion Laboratory (JPL) in California, US. They are used to working with Curiosity that is so far from Earth, with an average distance of 225 million kilometres. However, how does the arrangement affect the work of the mission team and Curiosity?

Curiosity Mars rover was launched on 26 November 2011 and after 9 months landed successfully on Mars on 5 August 2012. Curiosity was set out to answer a question: Was there life on Mars? It continues to dig out the answer by exploring the rocks, soils and atmosphere and analysing the contained chemicals and minerals on Mars. It has been working for 2746 sol (sol is the short form of Mars solar day, the time for Mars to rotate once and equals 24 hours 39 minutes and 35.244 seconds, which equals around 1.0275 Earth day).

The mission team and Curiosity Mars rover communicate through sending and receiving radio signals and the mission team sends commands to the Curiosity to work. Since the transmission of the signal takes time as it needs to travel for such a long distance, the mission team programmes a sequence of actions for the rover and the sequence may involve 20 people developing and testing commands together at the laboratory. On 20 March 2020, it was the first time that nobody on the team was working at JPL as each of the team was working remotely from home. They brought with them communication tools such as headsets home as far as they could and kept intensive communicating with scientists and engineers by utilising multiple video conferencing and messaging apps online. The lack of high-performance computers and requiring extra effort in communication have made the tasks more challenging. However, the team still devised the commands and Curiosity executed without a hitch. According to the team, the tasks took just one or two more hours than it normally does. They were presented a problem and they figured out how to make things work. This is what NASA termed "can-do spirit".

No matter how difficult we all have been through, together we can embrace this "can-do spirit" to cope with those unique and uncertain situations and figure out solutions to work our way.

P.S. NASA targets to launch a new Mars rover, Perseverance, in July 2020, and Curiosity may stop its operation. Space Museum will give a review of this extraordinary exploration vehicle in the upcoming issue of the Newsletter. We will also have an exhibition to introduce Perseverance in July.

Curiosity took selfie on Mars on 11 October 2019.
Image credit: NASA

Published on 3 May 2020

Uneven Expansion of the Universe?Top


The "Cosmological Principle" states that the universe is homogeneous and isotropic, which means everything looks the same in all directions on a sufficiently large scale, including the expansion rate of the universe which should be the same in any direction. This assumption is a fundamental concept in modern cosmology. However, a latest study reveals that this assumption may not be true.

The research team estimated the X-ray luminosity of distant galaxy clusters from the temperature of their gas. On the other hand, they calculated the expected X-ray luminosity of the same galaxy clusters with the effect of the expansion of the universe. The rate of expansion of the universe can hence be found after comparison. By collecting data form galaxy clusters in multiple directions, the expansion rate of universe in different directions can be deduced.

The Big Bang theory, as the mainstream cosmological model widely supported by astronomers, indicates that the universe is expanding in all directions evenly, but the result of this study reveals that the expansion rate might be higher in some directions. However, more evidence is needed before calming further conclusion. If the expansion of the universe is indeed not the same in all directions, it will be a big challenge for cosmology, and we may even need to build a new cosmological model.

Image credit: NASA/CXC/Univ. of Bonn/K. Migkas et al.

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Published on 27 April 2020

Hubble Space Telescope's 30th AnniversaryTop


The Hubble Space Telescope (HST) turns 30 on this Friday (24 April)!

HST is jointly operated by NASA and European Space Agency (ESA) and is one of the most important observatories in history. Since 24 April 1990, HST keeps orbiting around the Earth 24 hours a day, including on our birthday. It has made over 1 million observations and sent us numerous stunning images, transforming our understanding of the universe.

NASA is celebrating HST's 30th anniversary with a special event that allows us to find photos HST took on our birthday. These stunning images include the details of various planets, the key moment of birth and death of stars, and many others.

For instance, on the birthday of the Space Museum, the HST captured thousands of galaxies, some of which are as far as 12 billion light-years away. This image is part of the results of the Great Observatories Origins Deep Survey (GOODS) which enables astronomers to study the formation and evolution of galaxies in the distant, early Universe. Apart from our Milky Way Galaxy, there are zillions of galaxies out there in the Universe. Each galaxy contains billions of stars and it is possible an exoplanet that harbours life is just hanging out there! Want to know what did Hubble look at on your birthday? Just click on the link

On this important day, we wish to express our gratitude to HST for its great contributions to astronomy over the past 30 years. We believe there is still many more to come and let's enjoy the journey of exploring the vast and mysterious universe together!

Image credit: NASA

Published on 22 April 2020

Exoplanet Where It Rains IronTop


Raining is an important natural event that nourishes life... Hold on, would this sentence still be true if it is "iron rain" instead of "water rain"? Wow! The plot of raining molten iron should only appear in the sci-fi thriller...

It is possible to have "iron rain" in reality, but you don't need to worry as it is not a natural phenomenon on Earth. By using the European Southern Observatory's Very Large Telescope, astronomers observed an exoplanet WASP-76b that keeps extreme weather in which there may be "iron rain". The self-rotation period of WASP-76b and the period of it to orbit around its host star are the same. Hence, the same side of it always faces its host star. The side facing the host star is always in the daytime and may reach a temperature of more than 2,400 degrees Celsius, high enough to vaporise metals. The other side of it is always at night, the temperature on the night side can drop to about 1,500 degrees Celsius. The temperature difference between the two sides of the planet generates strong winds, bringing "iron vapour" from the day side to the night side. Vapour condenses into liquid in a lower temperature environment, causing the "iron rain".

Would iron rain nourishes any extraterrestrial creature?

Hence, the same side of the Moon always faces the Earth. This phenomenon is called "tidal locking", which is quite common in the universe.

More information:

Photo credit: ESO/M. Kornmesser

Published on 20 April 2020

50th Anniversary of Apollo 13Top


Do you know what happened 50 years ago in the history of space exploration?

"Houston, we've had a problem here" is the well-known phrase uttered in space 50 years ago during the Apollo 13 mission, which has since then achieved legendary status in the annals of manned space exploration. Including Apollo 11's first successful moon landing in 1969, there were altogether seven missions that put 12 astronauts on the Moon and returned them safely to the Earth. On 11 April 1970, the Apollo 13 mission began with the launching of a Saturn V rocket with three astronauts and the Apollo spacecraft at the Kennedy Space Center. While everyone expected the mission to be an uneventful one, an oxygen tank in the spacecraft exploded at around 55 hours after liftoff. The original landing-and-return mission instantly became a rescue operation. With ingenuity and cool heads, the crew members worked restlessly with the Mission Control to come up with makeshift modifications to the spacecraft and landing sequences so as to reduce electrical consumption and conserve enough oxygen for the spacecraft to loop around the Moon en route back to Earth At last, the crew members splashed down safely in the Pacific Ocean on April 17, six days after launch. The ordeal of the three Apollo astronauts was a story of turning a near-tragedy into triumph. The saga was subsequently adapted to make the film Apollo 13 (1995), a smash hit that unfolds the incident in vivid details on large screen.

The Apollo 13 mission is often dubbed "a successful failure" by NASA. Although the lunar landing part was aborted, the experiences gained in the mission would help NASA to stipulate more stringent safety standards for future space exploration. To commemorate the 50th anniversary of the Apollo 13, NASA has launched a series of online activities (for details, please refer to: Many resources are also available, including a commemorating video clip "Apollo 13: Home Safe" (

The journey of manned space exploration is never a smooth one. There will always be obstacles to overcome and hardships to endure. Uncertainties and challenges abound. The story of Apollo 13 reminds us that even though things are not working our way, we can still learn from these experiences. With resilience, resolve and keen minds just like the Apollo astronauts, one can turn misfortune into a blessing.

Photo credit: NASA

Published on 16 April 2020

Mystery of Betelgeuse's DimmingTop


The constellation Orion is no stranger to stargazers because it is one of the most recognisable constellations in the night sky. However, have you noticed in the past few months that Betelgeuse, which represents shoulder of Orion, looks slightly dimmer than before?

Betelgeuse is a huge star. If you put it in the position of the Sun, it will be large enough to swallow Jupiter. A huge red star like Betelgeuse is called a "red supergiant". It violently explodes when it dies, the light from the explosion can be seen at a very far distance. This phenomenon is called a "supernova explosion".

The sudden and unusual change in brightness of Betelgeuse has caused people to speculate that it is about to explode into a supernova. However, some researchers have indicated that the average temperature of Betelgeuse is much higher than that of a star going to explode, and proposed that its recent dimming may be due to the blocking of light by the dust gathered around that thrown from its surface.

Betelgeuse is about 700 light-years away from us. The light from this star takes about 700 years to reach us. It means that we are actually observing the star as it was about 700 years ago. The wonders of the universe are just so fascinating.

The images compare the constellation Orion in early 2012 and early 2020. The brightness of the red-orange Betelgeuse can be seen different. Photo credit: H. Raab / CC BY-SA (

The European Southern Observatory's Very Large Telescope captured a photo showing the brightness distribution on the surface of Betelgeuse and released via the website below:

Published on 14 April 2020

The Sixth Dwarf Planet?Top


Do you remember why Pluto was relegated from being a planet? Although Pluto is orbiting around the Sun like other planets, and has sufficient gravity to form a nearly round shape, it has not cleared the neighbourhood around its orbit. Hence, Pluto has been classified as a dwarf planet since 2006. However, we do not need to feel sad about it, as Pluto has some other dwarf planet friends in the Solar System, including Ceres, Haumea, Makemake and Eris.

Recently, astronomers have made a new discovery, which may add a dwarf planet companion to Pluto. This potential companion is called "Hygiea". It is the fourth largest celestial object in the asteroid belt. Astronomers discovered it in 1849, but not until the aid of European Southern Observatory (ESO)'s Very Large Telescope (VLT), we are able to observe the surface of Hygiea for the first time in high resolution, and calculate its shape and size. Astronomers found that Hygiea is spherical in shape, which may meet the definition of a dwarf planet. If it is successfully "upgraded", it will become the second dwarf planet in the asteroid belt after Ceres. We are glad that Pluto may make a little new friend!

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Photo credit: ESO/P. Vernazza et al./MISTRAL algorithm (ONERA/CNRS)

Published on 8 April 2020

Venus and the Pleiades EncounteredTop


A fantasy encounter was appeared on the sky in the past few days. Earth's neighbour, Venus, passed in front of the Pleiades (also known as the Seven Sisters) star cluster in the constellation Taurus, made this bright cluster into an "Eight Sisters"! Many overseas astronomy enthusiasts have taken pictures of their close encounter.

Venus is one of the planets in the Solar System, its position on the celestial sphere changes every day; the Seven Sisters is an open star cluster composed of distant stars, its position on the celestial sphere almost doesn't change. In the last weekend, Venus was passing in front of the Seven Sisters. Unfortunately, the weather in Hong Kong was bad, we were not able to watch this encounter. However, we can still see the bright Venus in the western sky during the evening in the next two months. Please enjoy if you are interested!

In fact, Venus orbits 13 times around the Sun for every 8 orbits of Earth (The Earth-Venus system performs an orbital resonance of 8:13). Hence, for every 8 years, Earth and Venus will appear an almost the same relative position. The last time when Venus passed closely in front of the Seven Sisters was in early April 2012. Can you guess when will be the next "Eight Sisters" reunion?

Photo credit: Fred Espenak

Published on 6 April 2020