Astronomy Picture of the Day

Explanation: Sometimes the sky itself seems to glow. Usually, this means you are seeing a cloud reflecting sunlight or moonlight. If the glow appears as a faint band of light running across the whole sky, you are probably seeing the combined light from the billions of stars that compose our Milky Way Galaxy. But if the glow appears triangular and near the horizon, you might be seeing something called zodiacal light. Pictured above, zodiacal light is just sunlight reflected by tiny dust particles orbiting in our Solar System. Many of these particles were ejected by comets. Zodiacal light is easiest to see in September and October just before sunrise from a very dark location.