The rich and reliable Geminid meteor shower is active from 4–17 December and predicted to peak between 2h and 23h UT (2am and 11pm GMT) on Saturday the 14th this year. However, these bright and slow-moving shooting stars will have to compete with a waning gibbous Moon just two days after full some 12 degrees away from the radiant (the apparent point of origin for the meteors, which is an effect of perspective) near star Castor in the constellation of Gemini. Were it not for the Moon’s glare, you could expect to see a meteor every minute at the shower’s peak viewed from a rural location. AN graphic by Ade Ashford.For those devotees of celestial firework displays, December contains arguably the best of the three great annual shooting star displays – the Geminids (the other two are the Quadrantids in January and the August Perseids). This rich and reliable meteor shower is predicted to peak between the hours of 2am and 11pm GMT (02–23h UT) on Saturday, 14 December 2019.
Origin and visual appearance
The Geminids originate from debris shed by the mysterious crumbly “rock comet” 3200 Phaethon. Earth ploughs through swarms of these particles strewn along the comet’s orbit from 4 to 17 December each year. The debris enters our planet’s atmosphere at speeds of around 35 kilometres per second (78,300 mph) and friction heats air molecules along the particle’s track creating the flash of incandescence that we call a meteor.
Under optimal conditions away from sources of urban light pollution you could conceivably see up to a hundred shooting stars per hour at the time of peak activity, but since the shower’s peak occurs two days after full Moon this year, the fainter meteors will be lost in moonlight. However, the Geminid shower offers a high proportion of bright naked-eye events with slow-moving shooting stars that can still be seen from rural areas under clear skies.
When to see the most meteors
AN graphic by Ade Ashford.The Geminid radiant (the region of sky where the shooting stars appear to originate) lies near Castor in the constellation of Gemini, the upper star of the celestial twins for Northern Hemisphere observers. Gemini rises in the northeast as darkness falls in the UK and lies highest in the southern sky around 2am local time. The radiant remains above the horizon throughout the hours of darkness in the British Isles.
If you can stay up, the brighter meteors tend to peak around midnight because we are then facing the direction the Earth is moving in its orbit and the relative speed of particles entering our atmosphere is higher. For observers in the British Isles, astronomical twilight fades to dark around 6pm GMT on 14 December, which coincides with the rising of the 17-day-old waning gibbous Moon, also in Gemini, just 12 degrees south of the radiant.
How to see the most meteors
The faintest meteors are the most plentiful, so to maximise your chances you should find a safe location that is as far removed from streetlights and other sources of light pollution as you can and allow at least 20 minutes for your eyes to become fully dark adapted. Try to obscure the Moon behind a wall or fence as its glare will detract from your night vision. Wear multiple layers of clothing with warm boots or shoes, gloves and a hat since a large proportion of heat is otherwise lost through the head.
A thermos flask of your favourite hot drink and a reclining chair is a good idea as you’ll be still for long periods during your vigil. Don’t concentrate on the radiant but at a point about 45 degrees (or twice the span of an outstretched hand at arm’s length) above it, halfway from the eastern horizon to overhead.