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Astro Bob

The Night Is Aglow With Natural Light, Too

29 Oct 2018, 22:18 UTC
The Night Is Aglow With Natural Light, Too
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On October 7, an astronaut aboard the International Space Station (ISS) shot this photograph while orbiting at an altitude of more than 250 miles (400 kilometers) over Australia. You can see the Milky Way across the middle of the frame, the Andromeda Galaxy at top. Starlight and airglow combine to provide enough light to find your way around even in areas of zero light pollution. NASA
What an incredible number of stars. The photo was taken with a Nikon D5 digital SLR and 24 mm lens and shows the Earth at night from orbit, the Milky Way and even the Andromeda Galaxy, 2.5 million light years away. Don’t overlook that delicate, orange rind of light surrounding the planet. That’s airglow, a form of natural “light pollution.”
Coming in orange, green and red, these diffuse bands of light stretch 50 to 400 miles into our atmosphere. The phenomenon typically occurs when molecules — mostly nitrogen and oxygen — are energized by ultraviolet (UV) radiation from sunlight. Atoms in the lower atmosphere are closely surrounded by other atoms and lose their extra energy by bumping into each other, but the upper atmosphere is thinner, with atoms less likely to collide. Those guys ...

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