August 18, 2009 in Keepers Log, Questions for the Keeper

Question for the Keeper: meteor shower radiant

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Last week’s Perseid meteor shower prompted the following question:
Why do meteor showers appear to radiate from single point in the sky?

Meteor shower particles are actually all traveling in parallel paths and at the same velocity, but they appear to an observer below to radiate away from a single point in the sky. This radiant point is caused by the effect of perspective, similar to railroad tracks converging at a single vanishing point on the horizon when viewed from the middle of the tracks. Due to the effect of perspective, shower meteors very close to the radiant will be quite short in length, while those some distance from the radiant can be quite long. Meteor showers are named for the constellation in the sky from which they appear to radiate. For instance, the Perseid meteor shower seems to originate from the region of the sky of the constellation Perseus. Each year in August, the Earth in its orbit around the Sun passes through the stream of the material left behind by the comet Swift-Tuttle. This comet detritus showers the Earth and rams into our atmosphere at approximately 37 miles per second (60 kilometers per second). Discovered back in 1862, Comet Swift-Tuttle made its most recent appearance in December 1992. Its orbit is highly elongated and takes roughly 130 years to make one trip around the Sun.

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