Mid December brings the peak of the Geminids – the best meteor shower of the year! Great news is that with New Moon occurring on Dec 11, we can look forward to observing this year’s Geminid peak without any significant moonlight interference
Which will be the best night(s)?
Geminid activity can be seen from around Dec 7 through to around Dec 16. Most of the activity occurs however over three or four nights near the peak. Although predictions quote a time on the afternoon of Dec 14th for the peak of the 2015 Geminids, the peak is actually quite broad and rates during the nights of both Dec 13-14 (Sun-Mon) and Dec 14-15 (Mon-Tue) will be close to the peak value. Rates should also be good during the night of Dec 12-13 (Sat-Sun) - which is good news for anyone unable to observe far into the nights of Dec 13-14 or Dec 14-15 due to next day work commitments.
When to observe each night
Geminid meteors appear to radiate outwards from a location near to the bright star Castor (Alpha Geminorum). The higher that this is in the sky, the more Geminids will be seen. With Gemini initially being rather low down, early evening Geminid numbers will be fairly low. However, Gemini climbs higher into the sky as the evening progresses and, as a result, observed Geminid numbers will increase significantly.
The Geminid radiant is highest in the sky shortly before 2am. Hence the best Geminid rates will be seen in the early hours of the morning, but good Geminid rates should be visible from mid evening onwards, so you may wish to start observing at 9pm or 10pm and then watch observed Geminid rates rise as the radiant approaches its high point. If work commitments prevent you from observing beyond midnight on Dec 13-14 or 14-15, you might still want to consider observing from 9pm until around midnight.
How many Geminids will you see?
In recent years, the peak Geminid ZHR has typically been in the 100-110 range. However, despite the impression given by many poorly written on-line news stories (some of which inflate the figure to 120), the observed rates that you see will not be as high as this ZHR value. Two main factors will impact the number of Geminids that you will see:
- The first is how much of the sky you can see. Choose an observing site that has a clear view of the sky so that meteors aren’t “lost” behind trees, etc.
- The second, and most critical, factor is the darkness of the sky background. If the sky is lit up by nearby streetlighting, the fainter Geminids will be “lost” against this bright background. Therefore, try to find as dark an observing site as possible
From a reasonably dark observing site with a good view of the sky, you can probably expect to be seeing 40-50 meteors per hour when the Geminid radiant is high in the sky during Dec 13-14 and 14-15. This figure is somewhat lower than the published ZHR value, but is nevertheless an impressive number of meteors.
Where to look in the sky
Don’t look at Gemini! Any meteors that appear there will be approaching almost head on and so their paths, projected against the star background, will be hard to spot. It is better to observe an area of sky around 25 degrees away from the radiant and about 50 degrees above the horizon (hold your hand at arms length and spread your little finger and thumb far apart. From tip to tip is approx. 25 degrees. So, one of these away from Gemini, and two of them above the horizon)
December nights with clear skies tend to be rather cold. Make sure that you are well wrapped up against the cold, paying particularly attention to your feet, knees, hands and head. You want to be focussing your attention on seeing meteors and not be distracted by the cold!
Let BAS and The Society for Popular Astronomy know what you see: Please mail your reports and images to Peter Truscott, via the Contact Page, or the SPA