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Moon and Mars

December 23, 2020

The night sky isn’t always dark. At various locations, and at various times of year, you might see glowing patches of light in the sky. The patches include auroras, airglow, noctilucent clouds, and a few others.

Patches of light glow in the skies of other planets, too. Mars, for example, has auroras — the shimmering curtains of light known on Earth as the northern and southern lights. And it also has airglow — a faint background light that’s related to auroras.

Not to get too confusing, but the Martian airglow is invisible — to the eye, anyway. That’s because it glows in the ultraviolet — wavelengths that are too short for the eye to see. But it’s an easy target for orbiting spacecraft.

Airglow is caused by the interaction between sunlight and Mars’s upper atmosphere. During the day, solar energy breaks apart molecules of nitric oxide. At night, the atoms of nitrogen and oxygen recombine. When they do, they emit ultraviolet energy.

Satellites have seen airglow encircling both of the Martian poles, especially during winter. And a recent study found the glow around the south pole forms a spiral. Scientists can’t explain why that’s the case. But they’ll keep an eye on it — an ultraviolet eye — to try to figure it out.

Look for Mars standing directly above the Moon as darkness falls this evening. It looks like a bright orange star. It’ll stand to the right of the Moon as they set in the wee hours of the morning.

Script by Damond Benningfield

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