Gegenschein: The glowing circle in the sky

The moon, stars, comets and planets aren't the only ones lighting up the night sky. Gegenschein glows in the sky every night – it's usually just too faint to be seen.

You're on the road in a dark and moonless night, hundreds of miles from civilization. When you look up into the sky, you see a faint, glowing spot. If you were a member of past generations, you might have followed it to find the new messiah. Living in a post Fire in the Sky world, however, you dive down and hope it finds someone else. No need to reach for that cyanide pill! It's not something looking to probe you. It's Gegenschein.

Gegenschein is the German word for ‘counter glow', and it appears in the section of the night sky directly opposite the sun. It's always there, but it's so dim that most of the time it's upstaged by the moon, light pollution, or even the collective glow of the Milky Way.

Considering what it's composed of, it's amazing that we see Gegenschein at all. It's hard to see entire planets, even when the sun is shining fully on them. When we see Gegenschein, we see dust. Space is filled with little particles brushed off by comets, planets and moons. It arranges itself in an elipse around the sun the way the orbits of the planets do. The sun shines on the dust, which reflect its light back to earth.

Since the dust surrounds us, why do we only see it at the point exactly opposite the sun.

Gegenschein: The glowing circle in the sky

Some say this is the result of the opposition effect. Many photos show a bright spot directly opposite the sun, or another light source. If light hits objects at an angle relative to the viewer, the viewer sees the shadows the objects cast. If it hits them head on, relative to the viewer, the viewer can't see any shadows, only continued brightness. This bright spot is always at the anti-solar point, relative to the viewer.

So if you are wandering through the woods and look up to see a giant glowing jellyfish, relax. Unless it's not at the anti-solar point in the sky. Then you're boned.

Via Skywatch, Weather Scapes, All the Sky, and Geospectra.