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Wednesday, August 12, 2009

Google and Perseids

Google marks August 12 as the day to commemorate Perseids, a prolific meteor shower associated with the comet Swift-Tuttle. The shower is said to be 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 primarily visible in the northern hemisphere. This 2009, it is said that the peak hourly zenith rate of the meteor shower is about 120, but fainter meteors will be washed out by a waning gibbous moon. There is no precise time as to when it will start appearing, but it is expected this August 12th at around 15.00 hours UT.

The Perseids are so called because the point they appear to come from, called the radiant, lies in the constellation Perseus. 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 passes 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 was pulled off from the comet in 1862. The rate of meteors originating from this filament is much higher than for the older part of the stream.

The meteors are actually leftover particles of the comet. As these small particles collide with the Earth's atmosphere, they burn-up, often creating a startling streak of light across the sky.

The Perseid meteor shower has been observed for about 2000 years, with the first known information on this meteor shower coming from the Far East. In early medieval Europe, the Perseids came to be known as the "tears of St. Lawrence."

Today, the mighty search engine Google.com, displays the Perseids Google logo. Clicking on the logo will automatically initiate a search query with the keyword "Perseids."

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