The Geminids or "Winter Fireworks" is widely regarded as the richest and most active of the annual meteor showers with this year's event peaking on night of December 13th/14th. During peak activity up to 120 meteors per hour can be seen under perfect conditions, including many bright ones. Of all annual showers, only the Perseids comes close to attaining such highs. This year's event promises to be a good one as the waning crescent Moon won't interfere. It may even be extra special as the parent asteroid, Phaethon, passes close by the Earth during the activity period.
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 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 - it's only 0.14 AU distant and much closer than the innermost planet, Mercury. However, at aphelion (the point of furthest distance from the Sun) the asteroid moves out to 2.4 AU, and therefore beyond the orbit of Mars.
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 found it on October 11, 1983. It has a diameter of only 5.1 kilometres (3.2 miles). On December 16, 2017, Phaethon will pass 0.0689 AU (10.31 million kilometres or 6.41 million miles) from the Earth. Just before closest approach, it will reach magnitude +10.7, and therefore bright enough to be spotted with an 80mm (3.1-inch) telescope.
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's located close to Castor (α Gem). This multiple star system has a combined apparent magnitude of +1.6, and is one of the brightest stars in the sky. Even brighter at magnitude +1.1, and located just 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 often appear bright. With a declination of +33 degrees, the radiant appears highest in the sky after midnight, and 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 the sky is dark enough. Due to the lower altitude of the radiant, observers from southern locations don't have it quite so good as their northern counterparts.
As with all meteor showers, it's best not to look directly at the radiant itself. The meteors can appear anywhere in the sky. To be certain you have a Geminid, trace the meteor trail and it should go all the way back to the radiant.
Geminids Data Table 2017
|Meteor shower name||Geminids|
|Meteor shower abbreviation||GEM|
|Activity||December 4th -> December 17th|
|Peak Date||December 13th / 14th|
|RA (J2000)||7hr 28m|
|Zenithal Hourly Rate (ZHR)||120|
|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|
|Last perihelion||October 7th, 2016|
|Notes||Phaethon approaches the Sun closer than any other named asteroid|