The annual Perseid meteor shower continues until 20th August, with the peak activity occurring during the night of 11/12th August. The maximum of the broad shower is expected to occur around dawn on 12th August.
Perseid Shooting Stars 2004
The Perseid meteors, or shooting stars, are small fragments of the periodic comet Swift-Tuttle, which enter the Earth's atmosphere at very high speeds - over 200,000 kilometres per hour - vaporising in the upper atmosphere at altitudes of about 100 km. Under ideal conditions, from a clear dark site, a peak rate of up to 80 meteors per hour may be achieved. The Moon will not interfere with viewing conditions this year, being in the waning crescent phase.
Comet Swift-Tuttle's revolution period around the Sun is about 130 years. The earliest sighting of the comet is believed to have been in 69 BC, and it was last near the vicinity of the Sun in 1992. The comet is in a fairly stable orbit and it sheds a fresh dust trail every time it reaches perihelion (closest distance to the Sun). Following many orbits of the Sun, the dust particles have now mostly spread uniformly around its orbit.
According to meteor researchers Esko Lyytinin and Thomas van Flandern, the Earth has probably never passed through a fresh dust trail from this comet. However, for this year they predict that the Earth will pass close to the dust trail emitted by Swift-Tuttle in 1862 exactly one revolution ago. They calculate the time of closest approach to be 9:50 pm on 11th August, at a distance of 190,000 km, about half the distance to the Moon. Lyytinin and van Flandern are expecting a moderately strong, relatively short shower of perhaps up to 100 faint meteors per hour for a short period either side of 10.00 pm.
David Asher of the Armagh Observatory is a little more cautious stating that with no meteor storm data in relatively recent times predictions cannot be calibrated to the same accuracy as the Leonid meteors. This makes computations somewhat uncertain as regards observed meteor numbers. He agrees, however, that it would be well worth observing during twilight on the evening of 11th just in case.
The Perseids radiant (the point from which the meteors appear to diverge) will be low in the north-northeast in the evening of 11th and high in the east during the early hours of 12th August. Observers in Europe and western Asia will be in the most advantageous locations this year.
For further information contact: John McFarland at the Armagh Observatory, College Hill, Armagh, BT61 9DG. Tel.: 028-3752-2928; FAX: 028-3752-7174; jmfarm.ac.uk
Esko Lyytinin's Predictions
David Asher on the Perseids
British Astronomical Association
Last Revised: 2004 August 12th
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