AMATEUR NATURALIST

Sky lights, far and near

The Iridium 33 satellite flashes in the sky over Athens, Greece, in June 2002. Iridium flares occur when the satellite's panels perfectly redirect solar or lunar light to an observer's eye on Earth. They can peak at about magnitude minus 8.4, much brighter to the eye than even Venus for a fleeting moment.
Courtesy of Anthony Ayiomamitis/www.perseus.gr
The Iridium 33 satellite flashes in the sky over Athens, Greece, in June 2002. Iridium flares occur when the satellite's panels perfectly redirect solar or lunar light to an observer's eye on Earth. They can peak at about magnitude minus 8.4, much brighter to the eye than even Venus for a fleeting moment.
Posted Aug. 11, 2012, at 5:24 p.m.

At any given moment on any given evening, the stars and planets seem motionless up there. If you watch for a little while, they all together shift position westerly because the Earth is rotating, but none of them seems to move independently of the others.

This is a trick of the eye, though. Everything is in motion even though it doesn’t look like it. If you keep track over days and weeks, you’ll see the planets (“wanderers”) move among the fixed stars. The motion seems gradual because they’re so far away. In fact, the stars are moving, too, but their distances are so immense that even after thousands of years they still appear fixed in relation to each other.

Occasionally something bright streaks out of the firmament and takes you by surprise, even when you’re watching for it. Sometimes it’s just a glint in the corner of your eye, and sometimes by luck you’re looking right at it. This motion is noticeable because the objects are, comparatively, so close.

The quick, short-lived streaks are shooting stars, or meteors — not actually stars but pieces of interplanetary grit smaller than your thumbnail that fall into the Earth’s atmosphere and heat up until they burst into flame for a second or so, sending out flares of light. Meteor showers occur regularly at different times of the year when the Earth travels through the debris-laden wakes of comets that anciently swept past. One of the brighter annual meteor showers is the Perseids, which have been lighting up the sky the past few August nights.

Sometimes larger rocks tumble in, too. These burn so bright and long they’re called fireballs, and they can be scary to see because some leave trails of smoke and fire in different colors. Big meteors that don’t burn completely and hit the ground are called meteorites. A meteorite about 5 inches wide crashed through a guy’s ceiling in Illinois a few years ago and demolished his computer printer. No one was hurt. Rarely a large meteorite will crash into the ground and leave a crater like the one near Winslow, Ariz. The nearly mile-wide crater formed when a meteorite about 80 feet wide struck the desert 20,000 to 50,000 years ago.

Not all moving objects are easily identified. Once when I was about 11, my heart leapt when I thought I saw a UFO. Peering from the back seat of my father’s Piper Cub one summer evening, I watched a tiny, dull pinprick of light slip across the stars. It must be a flying saucer, I thought.

It turned out to be a satellite. You can see them passing overhead if you’re lucky or know where to look just after sunset and just before sunrise. Thousands of them are orbiting the Earth hundreds of miles above us, and your eye can fairly readily pick up the sunlight bouncing off their antennas and silvery coverings. Some scoot across the sky fast, tiny dots of light, others more slowly.

Even though they’re human contraptions, they still have a sort of strange, ghostly beauty when their light strikes your eye. Little temporary blazes in the night with eternity for a backdrop. Little images of ourselves, I guess.

A computer program that predicts satellite passes is at heavens-above.com, and more information on satellite spotting is at the Visual Satellite Observer’s Home Page, satobs.org.

Dana Wilde will be reading from his book, “Nebulae: A Backyard Cosmography,” during the Maine Starlight Festival at 5:30 p.m. Thursday, Sept. 13, at the Southwest Harbor Public Library. “Nebulae” is available in paperback and electronically from Booklocker.com.

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