Astronomy Picture of the Day

Explanation: An unusual triangle of light is visible this time of year just before dawn. Once considered a false dawn, this triangle of light is actually Zodiacal Light, light reflected from interplanetary dust particles. The triangle is clearly visible in the above image taken from New Mexico, USA, in October. Curvature by the wide-angle lens makes foreground trees and a nearby less vertical than they really are. Zodiacal dust orbits the Sun predominantly in the same plane as the planets: the ecliptic. Zodiacal light is so bright this time of year because the dust band is oriented nearly vertical at sunrise, so that the thick air near the horizon does not block out relatively bright reflecting dust. Zodiacal light is also bright for people in Earth's northern hemisphere in March and April just after sunset.