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The Earth’s shadow cast on the atmosphere looks like a dark blue-purple band along the horizon. Above it glows the pale orange “Belt of Venus” created by sunset light reflecting off the atmosphere. Anti-crepuscular rays (shadows cast by clouds in the direction of the sun) are also seen. (Photo by Bob King)

Astro Bob column: Sights from the airplane

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Astro Bob column: Sights from the airplane
Duluth Minnesota 424 W. First St. 55802

Are you like me and try to get a window seat on your cross-country flights?

I always bring a book but never read it because of the constant but pleasant distraction of staring into space 35,000 feet above the surface of the planet.

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I just returned from a trip to Las Vegas. A combination of pure chance and a friendly ticket agent landed me window seats on both flights. Since it’s summer, the sky featured plenty of towering cumulus clouds, but as we approached the City of Sin, a dark presence grew across the eastern horizon. What resembled an approaching storm was actually the shadow of Earth creeping upward into the sky.

We see this all the time from the ground, but it’s not nearly as ominous when viewed from the extremely clear, dry air at high altitude. The color and darkness of the shadowy hump has not been altered in the photo — that’s exactly what it looked like. Its fuzzy appearance is caused by the atmosphere itself, which softens the shadow’s edge. This same shadow — cast across a much greater distance — cuts across the moon during a lunar eclipse and looks similarly woolly.

You can see Earth’s shadow from the ground anytime it’s clear around sunset or sunrise. Watch for a gray-purple band to appear in the eastern sky opposite the sun at sunset (or in the west at sunrise) for up to 30 minutes before fading away in the darkening sky. Because the shadow spans nearly 180 degrees with its highest point directly opposite the sun, you’ll get a visceral sense for how huge our planet is.

Maybe the craziest sight of all was seeing a gigantic city in the middle of the desert. As the plane descended, red, green and blue fireworks shot up like evanescent flowers everywhere across town.

While we’re all familiar with the Hollywood stars that frequent the city’s many casinos, I was thrilled to discover some actual stars — or at least their names — on city street signs.

Sure, there’s Mel Torme Way and Frank Sinatra Drive, but the astronomically inclined will smile wide when they turn down Aldebaran and Polaris Avenues. My daughter, Katherine, who I’d come to visit, graciously parked the car so I could get a few pictures.

On the return trip, I’d hoped we pass near enough Meteor Crater in Arizona but our trajectory lay well to the north. As I followed the looping Green River from canyon to canyon, an entirely different and unexpected crater crept into view from beneath the plane’s right wing — Upheaval Dome!

Younger sandstones form the outer rings of this belly button-shaped structure with older rocks heaped into a central peak on the crater’s floor. Originally thought to be a salt dome, shocked quartz and impactites found at the Dome in recent times clinch its extraterrestrial origin.

Last but not least, the ever-present gibbous moon shown hard and white against the super-blue sky. White, that is, until you compared it with the sunlit clouds below. They glowed far brighter, a sign that they reflect more light than the moon. Cumulus clouds have an albedo, a measure of the light reflected back by an object, of about 90 percent. The moon? Only 12 percent.

Of course, I didn’t travel to the West just to stare out a window, but it was a wonderful way to pass the time while captive aboard a plane. Lots of educational rubbernecking without having to keep your hands on the steering wheel.

Bob King is the News Tribune’s photo editor and amateur astronomer. Read more at astrobob.areavoices.com.

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