The Geminids or "Winter Fireworks" is one of the finest annual meteor showers with this year shower peaking on the nights of December 13 and 14. During peak activity up to 120 meteors per hour, many of them bright, can be seen under perfect conditions. However, sadly this year the waxing gibbous Moon will somewhat interfere with the Geminids during peak time. Of the other annual showers only the August Perseids comes close to attaining such highs.

Parent asteroid

The Geminids are unusual in that the source object is an asteroid, 3200 Phaethon. Together with the Quadrantids, they are the only major meteor showers not originating from a comet. Phaethon has an unusual orbit that brings it closer to the Sun than any other named asteroid, although there are several unnamed asteroids that do approach closer. At perihelion, the point of closest approach to the Sun, Phaethon is only 0.14 AU distant with the orbit being more like that of a comet than an asteroid. At perihelion it approaches the Sun to within less than half that distance of the innermost planet Mercury, while at aphelion (the point of furthest distance from the Sun) it is 2.4 AU distant and further from the Sun than Mars. It is perhaps a little strange that no cometary activity has ever been connected to Phaethon but nevertheless, the Earth passes through the debris field, resulting in the Geminids meteor shower.

Phaethon was the first asteroid to be discovered using images from a spacecraft. While investigating data from the Infrared Astronomical Satellite (IRAS), Simon Green and John Davies discovered Phaethon on October 11, 1983. Its diameter is only 5.1 kilometres (3.2 miles).

Radiant

The Geminids radiant or the point in the sky where the meteors appear to emerge from is very easy to find. At the time of peak activity, it is located very close to Castor (α Gem). Castor is a multiple star system that has a combined apparent magnitude of +1.6, making it one of the brightest stars in the sky. Even brighter at magnitude +1.1 and located only a few degrees southeast of Castor is Pollux (β Gem), the brightest star in Gemini. In 2013, Jupiter at mag -2.7 is located just southwest of Castor and Pollux.

Geminids Radiant and Star Chart - pdf format

What to expect

The Geminids are active from December 4th to 17th. They are slow moving meteors that are often bright. With a declination of +33 degrees, the radiant appears very high in the sky after midnight - even close to overhead - from mid-latitude northern latitudes. The best time to watch in 2013 is on the mornings of December 13 and 14, after or just before the Moon sets, until dawn. Observers from southern hemisphere don't have it quite so good due to the lower altitude of the radiant, but the temperatures are more pleasant and the shower is still excellent.

As with all meteor showers it is best not to look directly at the radiant itself; the meteors can appear many degrees away from it and even in a completely different area of the sky. To be certain you have seen a Geminid, trace back the meteor trail and it will go all the way back to the radiant.

Geminids Data Table 2013

Asteroid 3200 Phaethon (at epoch April 18, 2013)