Wednesday, August 08, 2007

Catch a falling star

This weekend (actually late Sunday night into early Monday morning) marks the peak of the annual Perseid meteor shower. If you are up late and can get away from city lights, why not go stare at the skies for a while and look for meteors?

On any given night, if you watch the skies long enough, you'll see a handful of meteors, anywhere from a few to several an hour, depending on how dark the skies are. These meteors are not really "falling stars," but are dust floating through the Solar System that happen to hit the Earth's atmosphere, and pieces of space junk (flecks of paint, pieces of insulation, parts of exploded rockets) falling back to Earth.

In a meteor shower, the Earth passes through the trail of debris left by a comet. Most of this debris is just tiny pieces of dust, though there is the occasional pebble-sized rock. These all burn up in the Earth's atmosphere; the smaller pieces make faint meteors, the larger pieces make bright meteors.

In mid-August, the Earth is passing through the trail left behind by Comet Swift-Tuttle, which passes through the inner Solar System every 130 years (last in 1992, next in 2126, so mark your calendars!). During this time, observers on earth can see 60 or more meteors an hour from a dark site, or about one a minute.

Note that last sentence. Sometimes people go out to look at meteor showers and expect to see meteors every second or two. This rarely happens. The Leonid meteors (seen yearly in November) make a "storm" like this every 33 years, last in 2001. But most of the time, a meteor shower rarely makes more than one meteor a minute. So you have to be patient, but know that you are seeing ten times more meteors than you would on a normal night!

The Perseids are a nice meteor shower. It is reliable, appearing about the same every year. They come in the summer, so the nights are warm enough for people to go outside. And they Perseids are visible for several days on either side of the best night, though with fewer meteors. So, if you have time on Saturday night/Sunday morning, you can still go out and look for meteors and likely see a good show.

Like most meteor showers, the Perseids are best viewed after midnight. This is because after midnight, you are on the side of the Earth that is plowing right into the meteors. Before midnight, you only see the rare meteor than can catch up to the Earth.

So, if you have time and clear skies, go out late one night this weekend and try to look for meteors. If you can get away from the city and have clear skies, I guarantee a nice show.

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