Sunday 20 October 2013

The Oroinid Meteors.

The Oroinid Meteors are a prolific meteor shower appearing in late October each year and peaking on the nights of 20-21 October, when the shower can produce 50-70 meteors per hour, originating in the constellation of Orion (above and to the right of Orion's right shoulder). This makes them both one of the more prolific meteor showers, and one of the easiest for an amateur enthusiast to locate the radiant of (apparent point of origin), though this year they will be at a peak slightly after a full moon on 18 October (the Hunter's Moon - last full moon before the autumn equinox - in the Northern Hemisphere).

The radiant of the Orionid Meteors. Astro Bob.

The shower is caused by the Earth passing through the trail of Halley's Comet, 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 Halley's Comet 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. Halley's Comet only visits the Inner Solar System once every 75 years, last doing so in 1986. It is currently 33.7 AU from the Earth (i.e. 33.7 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 approximate orbit of Halley's Comet. JPL Small Body Database Browser.

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