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See also: 2004 Perseids

This year's annual Perseid meteor shower takes place between the dates 17th July and 24th August, peaking on the night of 12/13th August, with a formal maximum in the small hours of Wednesday 13th August.

This is one of the best meteor showers of the year, with the maximum rate of meteors usually reaching about 80 per hour, although some years have seen rates as high as 200 per hour. The meteoroids, which are small fragments of the periodic comet Swift-Tuttle, travel through the Earth's atmosphere extremely quickly with almost half of them leaving persistent trains. This is the most famous of all meteor showers and rarely fails to provide an impressive display. The earliest record of its activity appears in ancient Chinese writings in AD 36.

The Perseids, are also known as the 'Tears of St Lawrence', since the peak of the shower occurs near the anniversary of his martyrdom in AD 258. The meteoroids encounter the Earth's atmosphere at over 130,000 miles per hour and vaporise at altitudes of about 60 miles. Most of the particles are the size of a grain of sand, but some may be as large as a pebble, and it is these that may cause a bright fireball.

Comet Swift-Tuttle takes approximately 130 years to make one circuit around the Sun, and sheds particles when closest to the Sun in its orbit. Its earliest sighting was in 69 BC, and it has been seen most recently both in 1862 and 1992. The orbit is relatively stable, the comet making one revolution for every eleven of the giant planet Jupiter. As a result of numerous passages past the Sun, the dust trails produced by the comet during each swing around the Sun have now been spread out almost uniformly around the orbit, resulting is a very predictable annual shower.

The radiant, the part of the sky from where the meteors appear to diverge, lies in the constellation of Perseus. The radiant rises in the north-east, and by the early hours of 13th August will be high in the south-east. When the radiant is high, the Perseids may be seen in almost any part of the sky. For the best view one should select a dark observing site having as little scattered light as possible. Observe the sky with your back towards the bright Moon or else observe from within the shadow cast by a building.

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

See also:
Gary Kronk's Site
Image of Swift-Tuttle

Last Revised: 2004 August 12th
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