Perseid meteors are gold medal event

After the spectacular opening fireworks of the Chinese Olympics comes one of nature's own finest displays - the Perseid meteor shower. In fact Earth began entering the dust stream that produces these shooting stars in July. But they will build to a peak in mid August when a single observer might see one or more a minute. The Perseids are dust particles ejected from Comet Swift-Tuttle which flare brilliantly as they enter the Earth's upper atmosphere and "burn up". They are one of the year's most reliable showers and a favourite for northern stargazers who can sit out and count them on warm summer nights. The meteors are expected to build to a rate of 80-100 an hour at maximum on 12 August - that is the number one might be expected to see with the unaided eye under ideal sky conditions if the radiant were directly overhead. The radiant is the point in the sky from which the meteors appear to diverge - an effect of perspective much like the way parallel lines of a rail track appear to converge into the distance. It lies in the constellation of Perseus which gives the meteor shower its name, but the meteors themselves can be seen in any part of the sky. The radiant is low in the sky when darkness falls but climbs steadily through the night and highest rates are likely to be seen in the early hours. Although the 12th is the night of maximum, it is worth watching on nights around that date too when rates are expected still to be very respectable. The waxing gibbous moon is low in the sky from mid-northern latitudes, setting around midnight. Conditions could therefore be ideal in the pre-dawn hours. The Society for Popular Astronomy meteor section reports that a Finnish meteor expert, Esko Lyytinen, believes that the Earth may encounter a denser meteoroid trail for perhaps an hour or so centred on 05h26m UT on 12 August. He suggests this could give another peak of 100-300, or even higher. The timing could particularly favour US sky-watchers. ©PAUL SUTHERLAND, Skymania.com • Skymania welcomes your comments on our stories! For more space reading, check out the Skymania stores in the USA, the UK, Canada and France. They are powered by Amazon so you can buy with confidence.

Great year to catch Perseid fireworks

Meteor watchers in the northern hemisphere are in heaven during the summer months when generally warmer nights coincide with a good period of meteor activity. The most famous annual shower, the Perseid shows its first signs in the next few days, building to a climax around August 12th. When at its peak, you should not have to watch a clear sky for very long before seeing one of its fast-moving "shooting stars". Conditions for observing the Perseids - so-called because the stream of comet dust that causes them appears to radiate from the constellation of Perseus - are excellent in 2007. Around maximum, when most people are keen to observe, the Moon will be out of the night sky and so will not drown out the spectacle with its light. This means, however, that it will be more difficult to view the shower's "early birds" in mid to late July. At best, the Perseids produce a ZHR, or zenithal hourly rate, of around 100 for a single observer. The figure is an estimate of the numbers that would be seen if the shower's radiant lay directly overhead. Don't expect to see more than a tiny handful during the early period of activity, however. There are other meteor streams active in July. According to the Meteor Section of the Society for Popular Astronomy, the Delta Aquarids are the strongest and show a peak ZHR or 15-20 arund July 28. Less active still is the Alpha Capricornids which may be seen from early July to mid August. Peak ZHR numbers only reach five or so most years, but when they do appear they are often bright and spectacular. ©PAUL SUTHERLAND, SpaceStories.com