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The Persieids are Back in Town
Comets >
Had a shower recently? Think about going outside tonight and taking one in. The peak to the annual Perseid Meteor Shower has arrived and under pretty good conditions. What are these shooting star visitors anyway, you may ask?
Our solar system has much more to it than meets the
eye. Beside one bright star and all those planets, there are asteroids
and comets and a menagerie of other tiny things left over from the creation
of the solar system.
One of these comets --- Swift-Tuttle by name --- buzzes around the sun
in a 130-year orbit that takes it close to Earth's orbit. Unknown to many,
it is the source of the Perseid Fireworks Show.
Comets shed material like a bad case of dandruff. As these comets made of rock and ice come close to the sun, they get warm. Millions of tons of water and other compounds get boiled off. This evaporation carries with it sandgrain-sized samples of schmutz that travel with the comet in its orbit, getting spread out over the eons into a long train of dirty debris.
It is that dross which gives us the spectacular shower.
As Earth orbits along nonchalantly it ploughs right through Swift-Tuttle's polluted orbit. Then kaboom zaloom! --- we get hit. When we run into the grit train our combined collision speed is about 40 miles per second! Which is precisely why they light up. Imagine driving down the highway at 40 miles per second when your dog next to you in the passenger seat decides to hang its head out the window. We have a fireball of flaming, charbroiled hot dog.
This is the demise that meets the tiny, unsuspecting grains of comet waste as they dive headlong into our atmosphere. Instant meteor.
Monday afternoon is when we pass through the thickest part of the river of rubble. Unfortunately our sun makes it rather difficult to see the meteors then. But not to worry!
The good side to this is that both Sunday night and Monday night should offer us good showers. The Moon will set early both evenings leaving a dark sky. But the best time to see the shower is --- ahem --- after midnight. Why?
Imagine driving your car through the rain. You are traveling forward, the rain drops are falling down from above. But the overall affect is that most of the drops are smacking into the front windshield, not the rear windshield.
It's like that with meteors. Before midnight our part of the Earth is like the rear window. Around midnight is when we spin around towards the incoming meteoroids. It is after midnight that, if predictions are correct, we should get about 60 per hour under dark sky conditions.
And the Perseids can be beautiful. The big ones burn themselves into your memory forever. Michael Seeds, professor of astronomy at Franklin and Marshall College, has watched them religiously for decades. "I have seen spectacular Perseids," he says, "rushing fireballs flashing colors and breaking into pieces." The Perseids really are a breed apart.
Get thee outside to the darkest place you can find with the fullest view of the sky. Lay back and look up. Weather permitting, they will light up all around.
Think about making this an annual event for you and your family. The warm summer evenings make it ideal. Says Dr. Seeds, "The most spectacular thing about the Perseids is their dependability. They have returned year after year since I was a little boy and I suppose they will continue for a long time after I am gone."
Questions or comments? Mark Ritter can be reached here.
Posted by Administrator at 2002.08.10 02:39 PM | Comments (0)
