Perseid Meteors in 2012
This years Perseid meteor shower, already in progress, continues until about August 24th. The peak of activity is expected to occur around midday on August 12th, with a possible all-sky maximum of perhaps 50100 meteors per hour visible during the nights of 11th/12th August either side of the shower maximum. However, a single observer may only see a fraction of this number, depending on the clarity of the sky and the fraction of the sky in view. Weather permitting, most people observing from a dark, clear observing site should expect to see around a dozen meteors per hour.
The Perseid meteors take their name from that of the constellation, Perseus, from where they appear to radiate. They are usually one of the most reliable annual meteor displays. The meteors are generally fast and bright, and may leave glowing 'persistent trains'. Assuming a clear sky, conditions for observing the peak are good this year, with a waning crescent Moon on the night of August 11th/12th and with a New Moon occurring on August 17th.
Most meteors are produced by comets, which shed trails of dust while passing through the inner solar system on their elliptical orbits around the Sun. In the case of the Perseids, the Earth encounters this dust at high speed over 200,000 kilometres per hour and this causes the small dust grains, with sizes ranging from typically a few millimetres up to a centimetre or more, to vaporize in the Earths atmosphere at a height of almost 100 kilometres. It is this vaporization, or burning up of the dust in the Earths atmosphere, that produces the visible meteor.
During the late evening of August 11th/12th, the constellation Perseus will lie low in the north-east. In order to see the Perseids to best effect (although it is possible to see some meteors while looking in any direction) you should select, if possible, a dark, clear site with a good vista towards the north or east. To observe meteors to best effect, you should always avoid light pollution, and allow time for your eyes to become accustomed to the dark. Then, look at an angle of about 45 degrees away from the radiant, in this case the rising constellation of Perseus, keeping the radiant near the edge of your field of view. To avoid fatigue, wrap up warm and recline in a comfortable chair under a rug or sleeping bag, if cold.
During the 1990s, when the Perseids parent periodic comet 109P/Swift-Tuttle last passed through the inner planetary system, there was much shower activity. Although the comet is now receding from the inner solar system, and will not return to the inner solar system until around 2126, the number of meteors has remained at a fairly high level. If you stay up until the small hours, look out for the bright planets Venus and Jupiter, which are both prominent in the eastern sky before dawn and this year help to mark the radiant, and also the waning crescent Moon.