The Geminids or "Winter Fireworks" is widely regarded as the richest and most active of the annual meteor showers with this year spectacle peaking on night of December 13th/14th. During peak activity up to 120 meteors per hour - many of them bright - can be seen under perfect conditions. Of the other annual showers only the August Perseids come close to attaining such highs.
In 2013, the glare from a waxing gibbous Moon significantly interfered with the Geminids around peak time, but this year's prospects are more favourable; the last quarter Moon doesn't rise until after midnight on peak day. By keeping the Moon out of view the most intense period of the shower can be observed with little interference.
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 and much closer to the Sun than innermost planet Mercury.
On the other side, at aphelion (the point of furthest distance from the Sun) Phaethon moves out to 2.4 AU and therefore beyond the orbit of Mars. It's perhaps a little strange that no cometary activity has ever been associated with Phaethon, but nevertheless the Earth passes through the dust 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).
The Geminids radiant or the point in the sky where the meteors appear to emerge is very easy to find. At the time of peak activity it's located very close to Castor (α Gem), a multiple star system that has a combined apparent magnitude of +1.6 and 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.
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 starting watching is before midnight on the evening of December 13/14th, although Geminid "shooting stars" can be seen as soon as it's dark enough. 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's 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 should go all the way back to the radiant.
Geminids Data Table 2014
|Meteor shower name||Geminids|
|Meteor shower abbreviation||GEM|
|Activity||December 4th -> December 17th|
|Peak Date||December 13th / 14th|
|RA (J2000)||7hr 28m|
|Parent body||3200 Phaethon (asteroid)|
|Notes||Together with the Quadrantids, they are the only major meteor showers not originating from a comet.|
Asteroid 3200 Phaethon (at epoch April 18, 2013)
|Discoverer||Simon Green / John Davies / IRAS|
|Discovery date||October 11th, 1983|
|Semi-major axis (AU)||1.27128|
|Orbital period (years)||1.43345|
|Longitude of ascending node (degrees)||265.267|
|Perihelion||March 15th, 2015|
|Notes||Phaethon approaches the Sun closer than any other named asteroid|