From 13 to 15 December, weather permitting, skywatchers will be looking up as the Geminid meteor shower reaches its peak, in potentially one of the best night sky events of the year.
At its peak and in a clear, dark sky, tens of ‘shooting stars’ or meteors may be visible each hour (the theoretical maximum under ideal conditions is about 120 an hour). Meteors are the result of small (millimetre- to centimetre-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 2am GMT the radiant will be almost overhead as seen 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 with the naked eye – no telescope or binoculars required.
Any light pollution will cut down the number of meteors visible, so the best views are on the outskirts of towns and cities and away from artificial light. If you need to find your way around or look at a star map, then you should use a red flashlight to preserve your night vision. Remember, that you should allow 20 minutes for your eyes to adapt to the dark.
Meteors in the Geminid shower are less well known than those at other times of year, probably because the weather in December can be less reliable. But those who brave the cold can be rewarded with a fine view. In comparison with other showers, Geminid meteors travel fairly slowly, at around 35 kilometres (22 miles) per second, are bright and have a yellowish hue, making them distinct and easy to spot.
The Geminid meteor shower will peak at around 6pm GMT on 14 December with the greatest activity being 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.
The spectacle provides an exciting opportunity for astrophotographers, so don’t forget to send your images of any meteors you manage to capture to firstname.lastname@example.org for a chance to be featured in the print edition of All About Space magazine!