A meteor shower, some of which are known as a "meteor storm", "meteor outburst", or "shooting star", is a celestial event where a group of meteors are observed to radiate from one point in the sky. These meteors are small fragments of cosmic debris entering Earth's atmosphere at extremely high speed. They vaporize due to friction with the air, leaving a streak of light that very quickly disappears. For bodies with a size scale larger than the atmospheric mean free path (10 cm to several metres) this visible light is due to the heat produced by the ram pressure (not friction, as is commonly assumed) of atmospheric entry . Most of the small fragments of cosmic debris are smaller than a grain of sand, so almost all fragments disintegrate and never hit the earth's surface. Fragments which do contact Earth's surface are called meteorites.
A Perseid (possibly 2) and Milky way
The Perseids (pronounced /ˈpɝsiːɨdz/ pûr'sē-ĭdz) are a prolific meteor shower associated with the comet Swift-Tuttle. The Perseids are so called because the point they appear to come from, called the radiant, lies in the constellation Perseus. Meteor showers occur when Earth moves through a meteor stream. The stream in this case is called the Perseid cloud and it stretches along the orbit of the Comet Swift-Tuttle. The cloud consists of particles ejected by the comet as it passed by the Sun. Most of the dust in the cloud today is approximately a thousand years old. However, there is also a relatively young filament of dust in the stream that boiled off the comet in 1862. The approximate rate of meteors originating from this filament is much higher than normal.
Observation
The famous Perseid meteor shower has been observed for about 2000 years, with the first known information on these meteors coming from the Far East. In early Europe, the Perseids came to be known as the "tears of St. Lawrence."
The shower is visible from mid-July each year, with the greatest activity between August 8 and 14, peaking about August 12. During the peak, the rate of meteors reaches 60 or more per hour. They can be seen all across the sky, but because of the path of Swift-Tuttle's orbit, Perseids are mostly visible in the northern hemisphere.
To experience the shower in its full, one should observe in the dark of a clear moonless night, from a point far outside any large cities, where stars are not dimmed by light pollution. The Perseids have a broad peak, so the shower is visible for several nights. On any given night, activity starts slowly in the evening but picks up by 11 p.m., when the radiant gets reasonably high in the sky. The meteor rate increases steadily through the night as the radiant rises higher, peaking just before the sky starts to get light, roughly 1½ to 2 hours before sunrise.
2007
The Perseid meteor shower peaked on the new-Moon night of Sunday–Monday, August 12–August 13 and could be seen from any place in the northern hemisphere. The Perseid meteors appeared to stream away from their radiant near the border of Perseus and Cassiopeia.
The meteor rate, for an observer at a dark-sky site in the northern temperate latitudes, increases to roughly 30 per hour in the predawn hours on Saturday, 45 per hour on Sunday morning, and 80 per hour before the sky starts to get light on Monday morning.
2008
The Perseids will next be active from July 17 to August 24, 2008, with their peak on the morning of August 12, 2008.
Thank Ref and Read more...Perseids - Wikipedia, the free encyclopedia, Meteor shower - Wikipedia, the free encyclopedia
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