Google 的图片都变了。

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From Wikipedia, the free encyclopedia

The Perseids (pronounced /ˈpɜrsiː.ɨdz/) is the name of 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. 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 the comet in 1862. The rate of meteors originating from this filament is much higher than for the older part of the stream.

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.[1] In early medieval Europe, the Perseids came to be known as the "tears of St. Lawrence." [2]

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 primarily visible in the northern hemisphere. As of 2009 the peak zenithal hourly rate is about 120, but fainter meteors will be washed out by a waning gibbous moon.