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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.

A Geminid meteor streaks through Ursa Major in 1998 (credit:- 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 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.

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 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.

Geminids Radiant and Star Chart (credit:- freestarcharts)

Geminids Radiant and Star Chart - pdf format(credit:- freestarcharts)

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.

View towards the southeast, just after midnight, from northern temperate latitudes on the morning of December 14, 2017 (credit:- freestarcharts/stellarium)

Geminids Data Table 2017

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
Zenithal Hourly Rate (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, 2013)

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 perihelionOctober 7th, 2016
NotesPhaethon approaches the Sun closer than any other named asteroid