Wednesday 8 August 2012

The Perseid Meteors.

The Perseid Meteor shower lasts from late July to early September each year, peaking on 12-13 August. This year this will coincide with a waning crescent Moon, hopefully making for a good display from many parts of the Earth; at the peak of the shower there can be 50-100 meteors per hour. The Perseids get their name from the constellation of Perseus, in which the meteors appear to originate.

Sky map showing the origin point of the Perseid Meteors; all the meteors appear to radiate from this point. NASA.

The shower is caused by the Earth passing through the trail of the Comet 109P/Swift-Tuttle, and encountering dust from the tail of this comet. The dust particles strike the atmosphere at speeds of over 200 000 km per hour, burning up in the upper atmosphere and producing a light show in the process. There is little chance of any meteors reaching the Earth, a meteorite that fell over California during the Lyrid Meteor shower in April is not thought to have been related to the shower, which is made of dust sized particles, but to have been the remains of an unrelated object, with a mass of up to 70 tonnes, striking the atmosphere at the same time.

The Earth does not need to pass close to 109P/Swift-Tuttle for the meteor shower to occur, it simply passes through a trail of dust from the comet's tail that is following the same orbital path. Comet 109P/Swift-Tuttle itself only visits the Inner Solar System once every 133 years, last doing so in 1992. It is currently 33.8 AU from the Earth (i.e. 33.8 times as far from the Earth as the Sun, further than the distance between Neptune and the Sun) on an eccentric orbit that takes it far bellow the plain of the Solar System.

The position of Comet 109P/Swift-Tuttle on 8 August 2012. JPL Small-Body Database Browser.

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