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Introduction

There float in the vast reaches of our Solar System swarms of sand bits and dust clods known as meteoroids. When these "space debris" tear into the Earth's atmosphere, air friction causes them to burn, forming momentary bright streaks that blaze across the sky. These are the meteors that we see from time to time.

Meteors often appear as sporadic lonely streaks that traverse somewhat random paths in the sky. This sporadic activity, which persists throughout the year, can account for about 10 visible meteors every hour on a clear night.

Meteors - Photo Courtesy NASA
Photo Courtesy NASA

A "meteor shower" occurs when our home planet encounters a relatively dense region of meteoroids in space. An unusually large number of meteors can then be seen streaming from a certain point in the sky known as the "radiant". Most astronomers believe that meteoroids are of cometary origin. They are leftovers from periodic comets or are even fragmented comet nuclei. This at least accounts for the fact that a particular group of meteoroids shares with its parent comet more or less the same orbit, which can remain relatively unchanged over eons. An immediate consequence is that our Earth makes periodic rendezvous with this meteoroid swarm, thereby culminating in a regular display of these celestial fireworks. To name a few, we have the Lyrids in April and the Geminids in December.

It is not uncommon that meteor showers are not spectacular at all, with the number of observed meteors barely surpasses the normal hourly rate. Needless to say, this may disappoint stargazers who hold high expectation, but it is definitely an unforgettable experience for those who have the luck to witness a truly enormous outburst.

During the small hours of November 13, 1833, people in Boston of the United States were terrified to see the sky blazed with thousands of meteors and fireballs streaming from the constellation Leo. (It was estimated that over 150 000 meteors were visible per hour). While many religious devotees believed that the Judgment Day had finally arrived, some even went so far as to commit suicide.

Major Meteor Showers in 2020

Shower Activity
(D/M-D/M)
Maximum
(HKT-D/M)
Zenith Hour Rate (ZHR) Suggested Observation Period Local Observation Condition
Quadrantid 28/12 - 12/1 4/1, 16:20 120 4/1, 1:00 – 6:00 Fair
Lyrid 14/4 - 30/4 22/4, 15:00 18 22/4, 23:00 – 23/4, 5:00 Fair
η-Aquariid 19/4 – 28/5 6/5, 5:00 50 6/5, 3:30 – 5:00 Bad
Perseid 17/7 - 24/8 12/8, 21:00 - 24:00 110 12/8, 22:30 – 13/8, 5:00 Unfavourable
Orionid 2/10 - 7/11 21/10, 13:30 20 22/10, 22:30 – 23/10, 5:30 Favourable
Leonid 6/11 - 30/11 17/11, 19:00 15 18/11, 2:00 – 6:00 Fair
Geminid 4/12 - 17/12 14/12, 8:50 150 13/12, 21:00 – 14/12, 6:00;
14/12, 21:00 – 15/12, 6:00
Excellent

Source of data: International Meteor Organization

* Local Observation Condition is divided into five levels, which are "Bad", "Unfavourable", "Fair", "Favourable" and "Excellent". The following factors would determine whether the observation condition is good or bad:

Observation Time: A darker sky is more favourable to meteor observation. If the meteor shower peaks in the period when the sun has not set, such as midday, or during sunrise or sunset, it is harder to see the trails of the meteors as they will be obscured by the bright sun. Also, due to motions of the Earth, the meteoroids collide head-on with the atmosphere at relatively higher speed after midnight, causing them to burn up vigorously. Thus, the meteors observed at dawn are usually brighter and easier to observe.

Moonlight: Moon is the second brightest object in the sky after the sun. When the occurrence of meteor peak is close to a full moon, the bright moonlight will obscure the dimmer meteors and affecting the number of meteors we can see with our naked eyes.

Radiant: Radiant is a point in the sky where the meteors appear to originate. As there are many skyscrapers in Hong Kong, when the radiant lies close to the horizon, the shower will be blocked by buildings easily, plus there are more haze near the horizon. Conversely, when the radiant is close to the zenith, it will favour the observation of meteors.

Reference:
1. https://bit.ly/341HooJ (Only Chinese version is available).
2. Out of the Blue: A 24-Hour Skywatcher's Guide P. 289-291 (https://bit.ly/2WcnhBo)

Please click to download the "Visual Meteor Observation Report Form"