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Blue Night

November 5, 2012

After the Sun goes down, a dome of light covers every city and town — the combined glow of the fixtures that illuminate streets, businesses, and our own yards. The light reflects off molecules and particles in the atmosphere, creating a glare that overpowers the natural lights in the night sky — the stars. In many big cities, the sky glow is so bright that only a handful of stars shines through it.

Like the light from the stars themselves, the sky glow is a blend of many colors. And thanks to changes in outdoor lighting technology, the color is starting to shift a bit to the blue end of the spectrum.

Blue wavelengths are just the right size to scatter in the atmosphere — which is why the daytime sky is blue. So blue wavelengths intensify the sky glow at night. And new LED lighting tends to be much bluer than some older types of outdoor lighting, such as the yellowish high-pressure sodium fixtures that line many streets today.

There’s some evidence that bluer light can affect a person’s natural circadian rhythm, and can cause problems for wildlife as well. And blue light makes it even harder to see the faint stars and galaxies sprinkled through the universe — a problem for astronomers, and for anyone else who wants to appreciate the beauty of a dark night sky.

There are still a few places in the U.S. where the sky remains nice and dark, and we’ll talk about a couple of those tomorrow.


Script by Damond Benningfield, Copyright 2012

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