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The Geminids or "Winter Fireworks" is one of the finest annual meteor showers with this year's shower peaking on the night of December 13/14. During peak activity up to 120 meteors per hour (Zenithal Hourly Rate) can be seen under perfect conditions. Of the other annual showers only the Perseids in August comes close to attaining such highs. Unfortunately, the full Moon in neighbouring Taurus will significantly interfere during peak time and wash out many of the meteors.

A Geminid meteor streaks through Ursa Major in 1998 (Yukihiro Kida)

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 Phaethon is only 0.14 AU distant with the orbit being more like that of a comet than an asteroid. It approaches the Sun to within less than half that distance of the innermost planet Mercury, while at aphelion it's 2.4 AU distant and further from the Sun than Mars. It's 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's located very close to Castor (α Gem). Castor is a multiple star system that has a combined apparent mag. of +1.6, making it one of the brightest stars in the sky. Even brighter at mag. +1.1 and located only a few degrees southeast of Castor is Pollux (β Gem), the brightest star in Gemini.

Looking southeast just after midnight on December 14th from mid-latitude northern locations (credit:- freestarcharts/stellarium)

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. Peak activity occurs on the night of December 13th / morning of December 14th during full Moon. A good tip is to position yourself so that the Moon is hidden from sight behind a building or something similiar and then scan the surrounding region of 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. 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.

Geminids Data Table 2016

Meteor shower nameGeminids
Meteor shower abbreviationGEM
Radiant constellationGemini
ActivityDecember 4th -> December 17th
Peak DateDecember 13th / 14th
RA (J2000)7hr 28m
Dec (J2000)+33d
Speed (km/s)35
ZHR 120
RatingBright
Parent body3200 Phaethon (asteroid)
NotesTogether with the Quadrantids, they are the only major meteor showers not originating from a comet.

Asteroid 3200 Phaethon (at epoch April 18, 2016)

Name3200 Phaethon
TypeAsteroid
ClassificationApollo (NEO/Pallas)
DiscovererSimon Green / John Davies / IRAS
Discovery dateOctober 11th, 1983
Aphelion (AU)2.40264
Perihelion (AU)0.13992
Semi-major axis (AU) 1.27128
Eccentricity0.88993
Orbital period (years)1.43345
Inclination (degrees) 22.2405
Longitude of ascending node (degrees)265.267
Last Perihelion October 7th, 2016
NotesPhaethon approaches the Sun closer than any other named asteroid