Monday, 11 August 2014

The Perseid Meteor Shower.

The Perseid Meteor shower lasts from late July to early September each year, and are expected to be at a peak on 12-13 August 2014, slightly after the Full Moon on 10 August, which may make the meteors harder to spot than when they occur at darker times of the month. 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 have their radiant (appear to originate).

The radiant of the Perseid Meteors. 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. 

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 35.6 AU from the Earth (i.e. 35.6 times as far from the Earth as the Sun, more than twice the distance between Neptune and the Sun) on an eccentric orbit tilted at 113° to the plane of the Solar System (or 67° with a retrograde orbit - an orbit in the opposite direction to the planets - depending on how you look at it), that takes it from 0.95 AU from the Sun (95% of the distance at which the Earth orbits the Sun) to 51.22 AU from the Sun (51.22 times as far from the Sun as the Earth, more than three times as far from the Sun as Neptune and slightly outside the Kuiper Belt, but only scraping the innermost zone of the Oort Cloud).

The orbit of 109P/Swift-Tuttle. Note that this is almost entirely below the plain of the Solar System. JPL Small Body Database Browser.

109P/Swift-Tuttle is next expected to visit the Inner Solar System in 2126, reaching about 22 950 00 km  (0.15 AU) from Earth in August of that year.

See also...


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