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 name derives in part from the word Perseides (Περσείδες), a term found in Greek mythology referring to the descendants of Perseus. The stream of debris is called the Perseid cloud and stretches along the orbit of the comet Swift-Tuttle. The cloud consists of particles ejected by the comet as it travels on its 130-year orbit. Most of the dust in the cloud today is around 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 earliest information on this meteor shower coming from the Far East. Some Catholics refer to the Perseids as the "tears of St. Lawrence", since August 10 is the date of that saint's martyrdom.
The shower is visible from mid-July each year, with the peak in activity being between August 9 and 14, depending on the particular location of the stream. 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 with all meteor showers, the rate is greatest in the pre-dawn hours, since the side of the Earth nearest to turning into the sun scoops up more meteors as the Earth moves through space. In 2009, the peak Zenithal Hourly Rate was about 120, but fainter meteors were washed out by a waning gibbous moon.
No comments:
Post a Comment