The nights between December 9 and 16 are marked by the best of all meteor showers – the Geminids. Up to 120 meteors per hour are visible during the shower’s peak on December 14 under dark skies, far from light pollution. This meteor shower, rich in bright, colorful meteors is also characterized by an unusually long period of relatively high activity – if you cannot observe on the peak night, you can see good numbers of meteors on December 12, 13 and 15! This year the peak of the Geminid meteor shower is expected on December 14 around 12h UT, but near-maximum rates persist for about a day, so everyone will have a good chance to see great meteor rates.
The activity graph below is updated every 15 minutes – click for details.
But the Geminids are not remarkable only due to their strength, they are also somewhat unusual as meteor showers go. While most meteor showers are born from comets, the Geminids appear to be bits of an asteroid. The parent body of the meteor shower is asteroid 3200 Phaethon. This 5-km rocky body orbits the Sun in an elongated elliptical orbit, which carries it out to the main asteroid belt at aphelion and as close to the Sun as 0.14 astronomical units at perihelion (more than twice as close to the Sun than Mercury!). 3200 Phaethon is a B-type asteroid, but recent observations with the STEREO spacecraft have revealed cometary activity near perihelion, so it is also referred to as a “rock comet”. It is hypothesized that the dust release is caused by thermal fracturing of the surface of the comet under intense heating near the Sun. 3200 Phaethon is a very interesting body and will certainly be the target of much future research!
How to observe the Geminids?
To observe the Geminid shower at its best, try to find an observing spot far from city lights. Light pollution will greatly diminish the number of visible meteors. You need no specialized equipment to observe the Geminids! Dress warmly, bring a reclining chair and watch the sky. You will not need to wait long for the first Geminid to appear!
The Geminid radiant is located in the constellation of Gemini, near the bright stars Castor and Pollux. On the peak night the radiant is just about a degree north of Castor (the northern twin). All Geminids will appear to radiate from this point in the sky. With 35 km/s the Geminids are medium speed meteors.
On the peak night the waning gibbous Moon rises around local midnight, so the evening hours will be dark. For mid-northern latitudes the radiant rises at dusk, so some Geminids may be seen even during the early evening hours. And these Geminids are special! As the radiant is very low, meteoroids skim the upper layers of the atmosphere nearly tangentially, creating long meteors that can traverse half of the sky or more! These meteors are called Earth grazers. As the radiant rises higher in the sky, the number of meteors increases. But even in the morning hours, as the Moon rises higher in the sky, still many Geminids will be visible, right up until dawn.
If you decide to do observe the Geminids, use the IMO major meteor shower observing technique. This way your data will be in a standard format, that can readily be used for analysis. Send us your data as soon after the observations as possible.
How to photograph the Geminids?
If you are new to meteor photography, this shower will be somewhat more difficult due to the bright Moon. But photographing meteors is fun, and it is easy. You will need a good camera – a DSLR, a mirrorless cam or a good bridge camera will do, a tripod and a remote release. Set the aperture to a wide setting, depending on the lens you have this is usually anywhere between f/1.4 and f/3.5. Set the camera to Manual mode (M) or Bulb (B), depending on what your camera offers. You would usually go for a relatively high ISO value, but since the sky will be bright you can stay at about ISO 800 or so. Now focus the image. Focusing your camera is absolutely crucial! There are few things as frustrating as out of focus photos! Use live view to focus on a star manually. Shift the focus around until the image of the star on your screen reaches minimum size. You can also use autofocus on the Moon, but do check your first photo if it is really in focus. Then set your exposure to about 10 – 15 seconds and use the remote release to make the photo (if you do it on your camera shutter button your photos will be blurred due to camera motion). Then find the exposure you are most comfortable with – this will depend on how bright you allow the photos to be (do not go too far or any meteors will be drowned out in the bright background) and how bright your sky is.