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Horseflies and Meteors

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Horseflies and Meteors

Like bugs streaking down the side window of a moving car, colorful Perseid Earthgrazers could put on a pleasing show after sunset on August 11th.



August 9, 2004: Splat! There goes another bug on the windshield.




Kids love the analogy: Earth, like a speeding car, races around the Sun sweeping up everything in its path. There are no insects in space, but there are plenty of meteoroids, little flakes of dust from comets and asteroids. They hit Earth's atmosphere--splat!--and disintegrate as fiery streaks of light called meteors.


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Coincidentally, many of the meteoroids hitting Earth will be about the size of tiny insects--as small as a flea or a mite. They make vivid streaks across the sky not because they're big, but because they are fast-moving. Perseid meteoroids hit our atmosphere traveling 59 km/s (132,000 mph).

Bugs tend to accumulate on a car's front windshield. Think about it: bugs rarely splat on the rear windshield. They can't fly fast enough to catch a car from behind. Likewise, meteoroids accumulate on the front windshield of Earth.

Earth has a windshield? It's our atmosphere, which protects us from solar wind and comet dust much as a car's windshield protects passengers from wind, rain and bugs. Earth's front windshield is the early morning sky. Earth circles the Sun dawn-side first, scooping up whatever lies on that side of the planet. That's why it's best to look for Perseids just before dawn.

To see the greatest number of Perseids this year, be outside before dawn on Thursday morning, August 12th, when Earth's front windshield is overhead.

Side windows, the ones to the left and right of passengers in cars, are good, too. Zooming down a bug-infested country lane, side windows don't collect many insects. But the ones they do collect are worth examining. Bugs that strike side windows do so at a shallow angle. They leave remarkable streaks, long and colorful.

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This also happens to meteors. For example, when the constellation Perseus (the source of the Perseids) hangs low near the horizon, meteors streaming from Perseus will skim the atmosphere horizontally, much like a bug skimming the side window of an automobile. Astronomers call these meteors "Earthgrazers." They tend to be long, slow and colorful.

Look for Perseid Earthgrazers on Wednesday, Aug. 11th, between 8:30 and 10:00 pm.

At that time, around sunset, Perseus will be hanging low in the northeast, perfectly placed to shoot Earthgrazing meteors over your head. Earthgrazers are rare. You might see only one or two, but that may be enough. A breathtaking Earthgrazer is the sort of meteor you're likely to remember years from now. And best of all, there's no gooey residue.

more information

The 2004 Perseid Meteor Shower -- (Science@NASA) Meteoroids in space since the Civil War will spice up this summer's Perseid meteor shower.

The Extraordinary Geomagnetic Perseid Meteor Shower -- (Science@NASA) A geomagnetic storm sparked auroras during the peak of the 2000 Perseid meteor shower. Could it happen again? Check


Perseids Photo Gallery -- (


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