Saturday, July 14, 2007

Falling Stars on Hot August Nights

Falling Stars on Hot August Nights
by Dave Adalian

About every 130 years or so, Comet Swift-Tuttle swings by Earth, circles the Sun, then heads back out into the dark, cold recesses of the Solar System.

As it sails along, the comet loses bits of itself, leaving a trail of tiny specks of ice and rock in its wake. As the years go by these comet crumbs spread out along Swift-Tuttle’s orbit into a huge doughnut-shaped cloud. Then, each August, Earth dives into that cloud, and the result is the annual Perseids meteor shower.

The Perseids are the year’s most reliable shower, with only a dud or two in the last decade. The 2007 show isn’t expected to bring the 400 or more meteors an hour seen in the early 1990s but away from city lights under a transparent sky, 80 to 100 an hour during the peak isn’t an unreasonable expectation.

The 2007 Perseids reaches an apex the night of August 12-13, with the greatest number of meteors predicted to fall between 10 o’clock and a half an hour after midnight.

The new moon will be absent from the sky, which is perfect for a meteor watch. Unfortunately, the peak’s timing is a bit off.

Best time to see meteors is around 2 a.m., when the sky overhead is facing forward with respect to Earth’s motion around the Sun, making it just like a car’s windshield. There are always more bug-splats on the front window than on the sides, and during the peak, the sky here will be like the side window of a car. So, like bug-splats on a side window, there will be fewer meteors but the ones we do see will be more like spectacular streaks than splats.

These meteors, known as earthgrazers, will come blazing in from the northeast, where the constellation Perseus--which gives the shower its name--will be rising, then shoot across the sky toward the opposite horizon.

Fortunately, the Perseids are very active around the peak. Rates of 40 meteors an hour the nights before and after are a real possibility. The Perseids is also a long shower that began July 17 and lasts through Aug. 24.

But, the best night for Perseids watching will be the night of the peak, and meteors will still be falling when 2 a.m. rolls around. And for those who stay up late, there’s the bonus of seeing Mars rise among the meteors around 1 a.m.


This column appeared originally in the Visalia (Calif.) Times-Delta and Tulare (Calif.) Advance-Register on July 26, 2007.


For the International Meteor Organization's 2007 Meteor Shower Calendar, which includes technical discussion of the showers and sky charts, click here.

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