A diagram showing how the meteors will appear to emanate from a radiant in the constellation of Gemini, located in the east in the evening sky. Credit: Greg Smye-Rumsby / Astronomy Now
From 13 to 15 Dec, weather permitting, skywatchers across the world will be looking up as the Geminid meteor shower reaches its peak, in potentially one of the best night sky events of the year. Tens of ‘shooting stars’ or meteors may be visible each hour (the theoretical maximum under ideal conditions is about 120/hr). Meteors are the result of small (mm- to cm-sized) particles entering the Earth’s atmosphere at high speed, burning up and superheating the air around them, which then shines as a characteristic short-lived streak of light. In this case the debris is associated with the asteroidal object 3200 Phaethon, which many astronomers believe to be an extinct comet.
The meteors appear to originate from a ‘radiant’ point in the constellation of Gemini, hence the name Geminid. By 0200 GMT the radiant will be almost overhead as seen from from the UK, making it ideally placed for observers. As a bonus, the Moon will not be present in the sky for most of the night during the period of maximum activity, so the prospects for a good view of the shower are excellent. And unlike many astronomical phenomena, meteors are best seen without a telescope and are perfectly safe to watch with the naked eye.
In comparison with other showers, Geminid meteors travel fairly slowly, at around 35 km (22 miles) per second, are bright and have a yellowish hue, making them distinct and easy to spot. According to the International Meteor Organisation the Geminids meteor shower will peak at around 1800GMT on 14 December, and the greatest activity is spread over a period lasting a day or more. In recent years, the shower has also become more intense as the gravitational influence of Jupiter and Saturn shifted a denser debris stream to be closer to the Earth.
Meteor watchers may want to look at different times during the night. Because of the rotation of the Earth, in the early evening, the edge of the cloud of debris that makes up the Geminids skims the atmosphere, leading to a few ‘Earth grazer’ meteors that can have long paths across the sky. Later on in the night, observers are looking up as their part of the Earth is facing right into the debris, so the number of meteors is usually much higher.
Mark Bailey, Director of the Armagh Observatory in Northern Ireland, added: “Unusually, the parent body for the Geminid meteors, namely Phaethon, currently appears to be an asteroid. However, its association with the Geminids tells us that it must once have been actively releasing meteoroids, perhaps as recently as hundreds or several thousands of years ago. Observations of the Geminids from around the world are beginning to help astronomers to understand how Phaethon and objects like it evolve over time.” http://www.ras.org.uk/news-and-press/2748-geminids-set-to-light-up-winter-sky-in-year-s-best-meteor-shower
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