Meteor showers of falling stars are one of the most anticipated celestial phenomena for astronomical enthusiasts, and the Geminid meteor shower, which is active in mid-December every year, is the closest meteor shower to this scene. On the eve of its arrival, let me introduce to you how to observe the meteor shower and what you need to pay attention to.
Meteors from the 2018 Geminid meteor shower appear over the United States
Causes of meteor showers
When a comet enters the inner solar system, the dust material ejected by the star's huge gravity and radiation will be scattered near the orbit. If the Earth passes through these material clumps as it orbits the sun, tiny pieces of gravel will enter the atmosphere in a short period of time, causing friction and light, forming many meteors. This phenomenon is a meteor shower, or meteorshower in English. In fact, the Chinese translation of "Meteor Shower" is not good. It is easy for people to imagine that there will be many meteors appearing at the same time. In fact, most meteor showers have a very small flow rate. The Geminid meteor shower is one of the many meteor showers that has a large flow all year round and is very stable.
The comet that produces the meteor shower "remains" material
So what is "large traffic"? We usually use ZHR to define the flow of meteor showers. ZHR is the abbreviation of Zenithalhourlyrate, literally translated as "zenith flow per hour", that is, assuming that the radiant point is at the zenith, the number of meteors that can be observed throughout the day every hour. Of course, the radiant point of a meteor shower rarely appears exactly at the zenith, so ZHR is only a theoretical flow value. If the ZHR value is M, the number N of meteors in the group that can theoretically be seen at the observation location and the horizon height h of the radiant point have the following simple relationship:
N=Msinh
In other words, the higher the altitude of the radiant point, the closer the number of meteors we can observe to the theoretical ZHR value. If the radiant point is not above the horizon, we will not be able to see the meteors in this meteor shower. Therefore, we cannot observe the "late night" meteor showers such as the Orionid meteor shower and the Leonid meteor shower in the first half of the night.
So what is the approximate ZHR of the Geminid meteor shower? The answer is only about 150. In other words, at about 2 a.m. in mid-December, when the Geminid meteor shower radiant point is closest to the zenith, we can see about 60 to 80 intra-group meteors per hour, averaging about one per minute. Don’t be too little, this is already the most suitable meteor shower for everyone to observe.
Schematic diagram of the Geminid meteor shower radiant point
The Geminid meteor shower best for public viewing
Next we introduce the Geminid meteor shower. In fact, this annual "final show" of celestial phenomena has quietly kicked off from late November, and the active period can last until late December, but the peak traffic only occurs from December 13th to 14th. Its radiant is located next to the bright star Castor in the zodiac constellation Gemini.
The Geminid meteor shower, the largest Quadrantid meteor shower in early January, and the largest Perseid meteor shower in mid-August have become the three major meteor showers in the northern hemisphere, because their radiants are all located in the northern hemisphere, making them more suitable for northern hemisphere observation. Among them, the best observation effect is the Geminids meteor shower. Because during its active period, the radiant rises in the east shortly after sunset, its swarm meteors can be seen almost all night long. As mentioned earlier, the better observation period for the Geminid meteor shower is around midnight.
Imagination of asteroid Phaethon
Schematic diagram of the orbit of asteroid Phaethon
Another notable feature of the Geminid meteor shower is the large number of bright bolide meteors, which is related to the composition and particle size of the dust that produces it. Some studies have shown that the parent "comet" that produced the Geminid meteor shower dust cluster is actually an asteroid numbered 3200 Phaethon, and this asteroid is likely to be a comet that is no longer active.
The meteoroid speed of the Geminid meteor shower is also relatively slow, about 35 kilometers/second, which is determined by the gap between the orbit of the dust mass and the orbit of the Earth. The slow speed of meteoroids means that the speed of most meteors is relatively slow, which is relatively more conducive to photographic observation.
When will you see the Geminid meteor shower this year? What do you think?
According to the current forecast, the maximum moment of this year's Geminid meteor shower is 9 a.m. Beijing time on November 14. Obviously, this period is not suitable for observation in our country. For everyone, the early morning of the 14th may be a relatively ideal observation time, but of course the ZHR should not reach 150. Of course, the observation of the Geminid meteor shower this year will also face the challenge of the "big moon". The 13th of this month happens to be the 13th day of the lunar calendar, the moon phase is close to the full moon, and it is located in the Taurus sky area, very close to the radiant point. Not only will there be fewer moon stars, but some fainter meteors will also be difficult to observe.
When it comes to observing meteor showers, you don’t actually need any special professional equipment. Especially with the lunar phase like this year, it will make it more difficult to photograph meteor showers.
For most people, the best way is to appreciate it directly with the naked eye. Because any telescope will narrow your field of view and miss many meteors. It is best for everyone to find a safe place away from urban light pollution, lie on a lounge chair or moisture-proof mat and enjoy the meteor shower.
To watch a meteor shower, you don’t have to just focus on the radiant point. When the radiant point rises higher, you may see meteors passing by in any direction. However, during the period when the Geminid meteor shower is active, it is already the middle of winter in most places in my country. If you want to observe the meteor shower outdoors for a long time, you must keep warm.
Li Xin, research librarian at Beijing Planetarium