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This year, the two-week long Geminid meteor shower peaks on the evening of 13 December. Although the shower does not produce the same high hourly rate of meteors associated with the Leonids, it is still a favourite with many observers, and is considered ideal for beginners.
Geminid meteors are often bright, with a yellowish hue, and tend to move relatively slowly across the sky. The meteor shower gets it name from the constellation of Gemini, from which the meteors appear to radiate. This Friday, by around 22:00, Gemini will be fairly high in the eastern sky for those observing from the UK. The radiant will be close to Pollux and Castor, the two brightest stars in the constellation of Gemini. Also in the sky will be the two gas giants, Jupiter and Saturn. The radiant can be found by drawing an imaginary line between the two planets and then looking just above the central point of that line.
The first recorded Geminids appeared in 1862, surprising sky watchers who saw 15 or so shooting stars each hour. Astronomers immediately began looking for a comet. Scientists have known for a long time that meteors are the result of left over dust from comets, burning up as it enters the Earth�s atmosphere. For more than a century astronomers searched in vain for the parent of the Geminids. Finally, in 1983, NASA's Infra-Red Astronomy Satellite (IRAS) spotted something. It was several kilometres wide and moved in much the same orbit as the Geminid meteoroids. Scientists named it 3200 Phaethon.
However, with this answer came another puzzling question; 3200 Phaethon appeared to be an asteroid rather than a comet. In fact, it is catalogued as a potentially hazardous asteroid (PHA) and approaches Earth�s orbit at only 8 lunar distances.
One possible explanation is that 3200 Phaethon is actually an extinct comet. It may have started out like any other comet, but its short period, sun-grazing orbit could have exhausted its supply of ices very rapidly. At its closest approach to the Sun, 3200 Phaethon gets nearer than the planet Mercury. All that may be left of the comet is an asteroid-like core of dust and rock.
Some studies have suggested that a number of NEOs may be dormant comets, which only appear to be asteroids. �The Geminids remind us that there is still much for us to discover about the nature of minor planets,� said Kevin Yates, Project Officer for the NEO Information Centre based at the National Space Centre in Leicester. �That is why up coming rendezvous missions such as Rosetta are so exciting, they offer an opportunity to analyse these objects in a detail that is not possible from Earth�.
More info: American Meteor Society
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