Every year amateur astronomers look forward to one particular event during August, the peak of the famous Perseids meteor shower. The Perseids are a very old stream; they have been observed for over 2000 years and are the best known of all periodic meteor showers. Observers often see many bright fast moving "shooting stars" including fireballs with the shower being extremely reliable - it rarely fails to deliver. The 2013 peak occurs on the night of August 11th / 12th and promises to be a good one. The 25% illuminated waxing crescent Moon will not interfere and up to 100 meteors per hour are predicted from a dark observing site.
Discovery and Parent Body
The Perseids meteor shower is associated with comet 109P/Swift–Tuttle or as it's more often known comet Swift-Tuttle; a Halley-type object with an orbital period of 133 years. The Perseid cloud consists of particles ejected by the comet and stretches along the comet's orbit. It's believed that most of today's dust in the cloud is about 1000 years old, although some parts may be considerably younger. When the Earth passes through a replenished area the meteor rate is increased compared to the older part of the stream.
The Perseids were first recorded by Chinese observers in 36 AD with comet Swift-Tuttle independently discovered by Lewis Swift on July 16, 1862 and by Horace Parnell Tuttle on July 19, 1862. Computations of the orbit of the Perseids between 1864 and 1866 by Italian astronomer G. V. Schiaparelli revealed a very strong resemblance to the recently discovered comet and this was the first time a meteor shower had been positively identified with a comet. The years either side of perihelion, usually exhibit higher rates of Persieds meteors, as was the case during the last perihelion in 1992. Swift-Tuttle on this occasion was visible from Earth with binoculars.
This meteor shower gets the name "Perseids" because it's radiant is located in the constellation Perseus. The radiant, the point in the sky where the meteors appear to originate from is positioned at right ascension (RA) 02hr 27m and declination (DEC) +58 degrees. This is close to the border with Cassiopeia and its well-known "W" shape asterism.
The meteors are visible from about July 17th to August 24th with rates starting low, gradually building up to the peak date, before falling off again afterwards. The shower is best seen from the northern hemisphere where the radiant appears high towards the northeastern part of the sky. At peak time, up to 100 meteors may be observed per hour.
For those located in the southern hemisphere, the Perseid radiant is either very low down or even never climbs above the horizon. This considerably reduces the number of meteors likely to be seen, although it's possible to see a few meteors per hour coming up from the northern horizon.
The star chart below shows the location of the Perseid meteor shower radiant.
The best night to observe is August 11th / 12th although good Perseid rates will also occur on August 12th / 13th and to a lesser extent on August 10th / 11th and August 13th / 14th. To spot as many Perseids as possible the best advice is the find a dark observing with an unobstructed view of the sky. Then scan a large area of sky surrounding the radiant but not directly at the radiant. The reason is that even though the meteors originate from the radiant, they usually appear many tens of degrees in the sky from it.
Although the Zenithal Hourly Rate (ZHR) for the Perseids is 100, this is number of meteors visible from an ideal location, free of light pollution when the shower radiant is located directly overhead. In practice rates observed are lower, but nevertheless dozens of meteors per hour should still be visible.
And finally, enjoy the spectacle!
Perseids Data Table 2013
|Meteor shower name||Perseids|
|Activity||July 17th -> August 24th|
|Peak Date||August 11th/12th|
|RA (J2000)||02hr 27m|
|Notes||Prolific meteor shower that was first recorded in 36 AD|
Comet 109P/Swift–Tuttle Data Table (at epoch April 18, 2013)
|Classification||Halley-type comet (NEO)|
|Discoverer||Lewis Swift / Horace Parnell Tuttle|
|Discovery date||July 16th, 1862|
|Orbital period (years)||133.285|
|Last perihelion||December 11th, 1992|
|Next perihelion||March 26th, 2126|
|Notes||Also known as Comet Swift-Tuttle|