What is Gegenschein?

Gegenschein or counterglow is a faint bright spot in the night sky centred at the antisolar point, ie. the abstract point on the celestial sphere directly opposite the Sun from an observer's perspective. This means it is a point above the horizon where the Sun is opposite and below it, and vice versa. It is seen as a faintly lit spot in the sky, opposite where the sun is.

This optical phenomenon is caused by the backscatter of sunlight by interplanetary dust.

Gegenschein