Friday, August 9, 2013

The meteor family of words

Sometimes words that describe the natural world come in a rather confusing clump. I'm hoping to explore many of these groups of words describing interrelated or similar concepts. Because one of the best-known meteor showers, the Perseids, is peaking this weekend, let's start with the meteor family of words.

A meteor, of course, is that thin needle of light streaking through the night sky that we also know as a shooting star. Meteor showers occur when Earth passes through the swath of debris left by a comet. We've identified the comets that have spawned various meteor showers; the Perseids are the leftovers of Comet Swift-Tuttle. The showers themselves, by the way, are named for the constellation from which they appear to come, in this case Perseus.

Several other words are also used to describe interplanetary dust and fragments more precisely.
  • A meteoroid is a bit of debris that would become a meteor if it entered Earth's atmosphere. They're much smaller than asteroids and range from tiny dust grains to pieces about one meter across—essentially the dust bunnies of the solar system on up to things the size of maybe a washing machine. Think of asteroids and planetoids and remember that all three are out in space.
  • A meteorite is a meteor that survives its journey through the atmosphere. Most meteors are so small that they simply vaporize in the atmosphere, but the larger ones can make it down to the surface. Both meteorites and meteors add their mass to Earth's; it's hard to tell exactly how much mass this amounts to, but estimates range from 37,000 to 78,000 tons per year, most of it from tiny bits of dust.1
  • A particularly big, bright meteor is sometimes called a fireball. The best-known recent example of this is the spectacular fireball that streaked across the sky near Chelyabinsk, Russia in February 2013. A large meteor that explodes in the atmosphere is called a bolide, from a Greek word meaning missile. The Chelyabinsk meteor broke up in the atmosphere and was so large that it's also called a super-bolide.
  • Sporadic meteors are random bits of space debris that are not associated with a particular comet. They might be fragments of asteroids that broke up, or bits of the moon or Mars that were ejected during an impact. Some of the latter even make it down to the surface sometimes; enough of these have been identified as coming from Mars that they are classified into different types.
The next time you're out under a dark sky and see a fleeting thread of light appear in the starry sky, remember that you're watching the end of a long space odyssey, signaled by the tiny quiet flash of vaporization as a bit of space dust becomes part of Earth.


1 Cornell Ask an Astronomer page

Learn more:

  • The American Meteor Society has an informative site with the latest news on meteor showers and fireball sightings.
  • We're lucky this year that the Perseids occur when the moon is a waxing crescent, so moonlight shouldn't be a problem. See the AMS's Perseid 2013 page for more information about viewing the shower.
  • If your skies are cloudy, you can listen to signals from the USAF Space Surveillance Radar on Space Weather Radio; you can hear a ping every time a Perseid flies over the radar.
  • Dr. Tony Irving of the University of Washington maintains a Martian meteorites page.

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