Western Slope Skies - Meteor Showers

Dec 4, 2015

Comet 17P/Holmes and Geminid meteor seen from San Francisco.
Credit Brocken Inaglory - This file is licensed under the Creative Commons Attribution-Share Alike 3.0 Unported, 2.5 Generic, 2.0 Generic and 1.0 Generic license.

A Primer on Meteor Showers

Typically, meteor showers occur when the Earth passes through particle clouds left by the passage of a comet.  The particles burn up in the Earth’s atmosphere, resulting in a brief streak of light.  The particles can range in size from dust to 33 feet in diameter.

The terms “meteor,” “meteoroid,” and “meteorite” are related, but are not identical terms.

Meteoroids are particles still in space and smaller than 33 feet.  Meteors are what we actually observe if a particle burns up in the atmosphere.  Typically these particle vaporize in the atmosphere and leave nothing solid behind at all.  Meteorites are the larger particles that reach the Earth’s surface.  Sometimes these are found and used for science.  

Very few meteors result in meteorites.  Perhaps millions of meteors occur daily.  Only 5,000 of these reach the Earth’s surface to become meteorites.  Further, only about 5 meteors per day are turned in for scientific study.  

A meteor that is brighter than any planet is a ‘fireball.’  A meteor that strikes the atmosphere at a shallow angle and returns to space is called an ‘earth grazing’ fireball.  A bolide is a fireball that explodes in the air.  They can be brighter than any object in the sky other than the Sun.

Occurring in December each year, the Geminid meteor shower is different.  While it still results from particles entering our atmosphere, the source is not a comet, but rather an asteroid.

This asteroid is designated 3200 Phaethon and is over 3 miles in diameter.  Discovered in 1983, Phaethon circles the Sun every 1.4 years, leaving more dust behind on each pass.

The Geminids can be an intense meteor shower and should peak around December 13 and 14.  While the best time to see a meteor is after midnight, you may be able to observe a Geminid early in the evening.  The best way to observe a Geminid meteor is to bundle up, find a dark location with a broad expanse of sky, lie comfortably on your back, and observe the sky for as long as you can take the cold temperatures.   Telescopes and binoculars are not needed for observing meteors.

Western Slope Skies is produced by members of the Black Canyon Astronomical Society.  This episode was written and recorded by Bryan Cashion.