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Armagh Observatory

A Good Year to View Geminid Meteors

This year's annual Geminid meteor shower is active during the period December 7 - 17, with the peak of activity occurring during the night of December 13th/14th. The Geminid shower is currently one of the best of the major annual meteor displays, usually having a high number of relatively bright, medium-speed (130,000 km per hour) shooting stars.

Under ideal conditions from a dark observing site, it is expected that there will be up to 120 meteors visible per hour for a few hours around the time of the peak. The peak occurs around new Moon this year. The Geminid radiant will be moderately high in the east in the late evening on 14th. Geminids travel at average meteor speeds, are moderately bright, yellowish with some leaving glowing trails (persistent trains) behind. The Geminid shower is notable also for providing occasional exceptionally bright meteors, called 'fireballs'.

Most meteors originate from comets, but in 1983, a potentially hazardous asteroid, (3200) Phaethon, was discovered by Simon Green and John Davies in data collected by NASA's Infrared Astronomy Satellite. Orbital computations revealed that this minor planet was following the same orbit as the Geminids, and was probably the parent body of these meteors and the first meteoroid stream to be found to come from an asteroid. The reason for this is still unclear, perhaps a collision with another asteroid in the remote past caused Phaethon to release a meteoroid stream. Currently, Phaethon can approach the Earth to within two million miles.

The Geminids were discovered in the 1862 by Robert Greg of Manchester and by the 1890s the number of bright meteors had increased dramatically by a factor of two. During the 1980s, hourly rates were noted to vary between about 60 and 110, while current rates range from 80 to 110. The reason for the increase in numbers is because the gravity fields of Jupiter and the Earth are changing the orbit of the meteoroid stream, pulling it from well inside the Earth's orbit to well outside. Radar observations have shown that the shower can be active as early as the end of November and as late as the end of December.

Other celestial bodies to look for while meteor watching in mid-December are the planets Jupiter (low in the southwest during the early evening), Mars (low in the east around midnight) and Saturn (moderately high in the southeast about 6.00 a.m.) The Orion nebula, under the three stars of Orion's belt and an active star-forming region approximately 1300 light years away, remains above the horizon throughout the night. The International Space Station will make a pass on December 14th from about 6.51 to 6.57 a.m. It will appear as a bright star-like object crossing moderately high from the southwest to the east.

For meteor observing, it is advisable to find a dark site, away from city lights and wrap up well in several layers of warm clothing.

FOR FURTHER INFORMATION PLEASE CONTACT: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfat signarm.ac.uk.

Last Revised: 2009 December 7th