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2021 Astronomical Events

 

There are plenty of astronomical events every year. The Hong Kong Space Museum stages a special exhibition at the foyer and online to introduce five spectacular events in 2021. The exhibition will offer observing tips on how to pick the best dates, times, locations and tools for observations.

The five spectacular events are: "lunar eclipses" on 26 May and 19 November, "Perseid meteor shower" in mid-August, "Geminid meteor shower" in mid-December and "serial phenomena of Jupiter's moons" on 15-16 August.

Venue: Foyer of the Hong Kong Space Museum
Exhibition period: Till 27 December 2021
Time: Please refer to the opening hours of the Museum
Free admission

Playback of the Online Lecture "2021 Astronomical Events" (conducted in Cantonese)

 
 
 

Total lunar eclipse (26 May 2021)
Partial lunar eclipse (19 November 2021)

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In the evenings of 26 May and 19 November, you may enjoy a total lunar eclipse and a partial lunar eclipse respectively in Hong Kong under favourable weather conditions. For the total lunar eclipse, the Moon will appear coppery-red near the moment of maximum eclipse. The Moon is below the horizon at the beginning of both eclipses, thus part of the eclipses is not visible in Hong Kong.

Ease of Observation

Easy

How to See?

With naked eyes or a telescope

  Total lunar eclipse
26 May 2021
Partial lunar eclipse
19 November 2021

When to See?

18:56 Moonrise
19:11 Total eclipse begins
19:19 Maximum eclipse
19:26 Total eclipse ends
20:52 Partial eclipse ends
21:50 Penumbral eclipse ends
17:37 Moonrise
18:47 Partial eclipse ends
20:04 Penumbral eclipse ends

Where to see?

A location with an unobstructed view of the sky and horizon in the east to southeast direction A location with an unobstructed view of the sky and horizon in the east to northeast direction

What to See?

The videos below simulate the telescopic and naked eye views of the two lunar eclipses observed in Hong Kong.

Total lunar eclipse (26 May 2021)

Partial lunar eclipse (19 November 2021)

Why?

Lunar Eclipses

Dimming of the Moon occurs during a lunar eclipse since the Earth blocks part of the sunlight when the Moon enters its shadow. The Moon appears coppery-red for eclipses of large magnitude. It is because the Earth's atmosphere scatters the blue component of sunlight away, leaving the red component which is refracted by the atmosphere and illuminates the Moon.

Perseid Meteor Shower (12 - 13 August 2021)
Geminid Meteor Shower (13 - 14 December 2021)

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Watching from a dark rural location with a wide field-of-view, you may be able to see 20 to 30 meteors per hour under favourable weather conditions. Try the nights before and after if weather permits.

Ease of Observation

Medium

Where to see?

Go to a dark place with little light pollution, such as a rural area. Light pollution causes a significant drop in the number of observable meteors. You may not even see a single one in urban areas!

Find a site with a wide field-of-view. The wider the view of the sky, the higher the chance to see more meteors.

What to See?

Perseid Meteor Shower

Geminid Meteor Shower

How to See?

Q: Should I gaze at the radiant?
A: Not necessarily. Meteors may appear anywhere in the sky. It is better to look everywhere.

Q: Why red light torches?
A: Red light is preferred for maintaining night vision. A red light torch can be easily made by covering a regular torch with layers of red cellophane, cloth or plastic bag.

Q: Shall I lie down and use naked eyes?
A: Yes. You'd better lie down enjoying a wide view of the sky and count the number of meteors with naked eyes.

Q: Shall I use a telescope?
A: No. The narrow field of view through a telescope decreases your chance of seeing meteors.

Why?

"Meteoroids" are natural debris and rocks sized between 0.03 mm and 1 m. A "meteor" is the streak of light crossing the sky resulting from the high-speed entry of a meteoroid into the atmosphere. A meteorite is a meteoroid falling to the ground. A "meteor shower" is formed when the Earth passes a swarm of meteoroids with similar orbits sharing a common origin.

To Know More

Click here to know more about how meteor "shines": Physics of meteor generated shock waves in the Earth's atmosphere – A review

Click here to know more about ZHR (Zenith Hourly Rate) calculation: Meteor stream activity

Serial Phenomena of Jupiter's Moons
(15-16 August 2021)

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A series of "transit", "eclipse" and "occultation" phenomena of all four Jupiter's Galilean moons happens within a few hours this night. "Mutual occultations" and "mutual eclipses" even occur between the moons. Mutual events are rare phenomena having a repeating cycle of roughly every six years.

Ease of Observation

Difficult

How to See?

Observe with an astronomical telescope of 20 cm aperture or more, with at least 200× magnification. A very stable atmosphere is required to observe the mutual events.

Where to see?

A location with an unobstructed view to the horizon in the east to southeast direction, and also in the southeast to southwest direction

What to See?

This videos simulate the telescopic view of the event between 17:41, 15 August and 03:10, 16 August 2021 (Hong Kong Time). (In this computer simulation, the positions of Jovian surface features such as the Giant Red Spot can differ from reality.)

Why?

Serial Phenomena of Jupiter's Moons

Jupiter's moons are in constant orbit around Jupiter. Changes in the relative positions of the Sun, the Earth, Jupiter and Jupiter's moons lead to one of the above three kinds of phenomena. Multiple phenomena can occur simultaneously.

Serial Phenomena of Jupiter's Moons

Serial Phenomena of Jupiter's Moons

The mutual events between the Galilean moons are rare because their orbits are tilted slightly towards the ecliptic plane (the plane of the Earth's orbit around the Sun). Therefore, for most of the time we would see them travelling in distinct orbits around Jupiter. However, as their orbital planes also wobble as the giant planet revolves around the Sun, for roughly every six years, we will see them edge-on, giving rise to the possibility of mutual occultations and eclipses among the moons. Multiple phenomena can occur simultaneously.