Perseid Meteors and Planetary Alignments

Map showing the radiant (apparent point of origin) of the Perseid meteors.

This year's Perseid meteor shower occurs between July 17th and August 24th. Peak activity is expected within two to three hours after midnight (BST) on the night of August 12th/13th.

This shower is usually one of the most reliable annual meteor displays of the year. During peak activity this year, up to 60 meteors per hour may be potentially visible in ideal sky conditions. However, a single observer may only see a fraction of this number, depending on what fraction of the sky is in view. The meteors are generally fast and bright - many leave glowing 'persistent trains'. Assuming a clear sky, conditions for observing the peak are good this year with New Moon occurring on August 10th.

During the 1990s, when the Perseids' parent comet passed close to the Earth, there was much activity during the shower. Since then the number of meteors arriving has decreased by a factor of about four, as the parent periodic comet, 109P/Swift-Tuttle, now recedes from the inner solar system before returning to the Earth's vicinity in the year 2126.

Comets are usually the sources of meteors, as they shed dust trails when they pass closest to the Sun. In the case of the Perseids, the Earth encounters this dust at high speed - over 200,000 kilometres per hour - causing the particles to vaporise in the Earth's atmosphere at a height of almost 100 kilometres and become visible meteors.

The Perseids emanate from the constellation Perseus, the radiant, which in the early morning of August 13th, will lie moderately high in the north-east. For general meteor detections, check Armagh Obsevatory's meteor camera system. To observe the Perseids you should select, if possible, a dark site with a clear vista looking towards the east. Allow your eyes time to become accustomed to the dark, and look at an altitude of about 45° keeping the radiant to the edge of your field of view. To avoid fatigue, recline in a comfortable chair under a sleeping bag, if cold.

Also, around the middle of the month, the planets Mercury, Venus, Mars, Jupiter, Saturn and Uranus are aligned approximately in a straight line in space. Mercury, Venus, Mars and Saturn are low in the evening sky after sunset, whereas Jupiter and Uranus rise in the east soon after dark and are best seen around midnight. There will also be an alignment of the waxing crescent Moon, Venus, Mars and Saturn on August 13th. However, with strong twilight conditions prevailing, Mars and Saturn may be difficult to spot.

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

Last Revised: 2010 August 2nd