False dawns demystified
Zodiacal light is the diffuse triangular patch that can sometimes be seen in the early hours. It’s so bright at certain times of year in areas with low light pollution that it can be mistaken for sunrise (hence its ‘false dawn’ moniker). But what causes it?
The glow is sunlight reflected and scattered across a region of interplanetary dust particles, known as the zodiacal cloud. Mostly made up of tiny debris from Jovian comets and asteroid collisions, it orbits our Sun in the same plane as the planets, spanning the inner Solar System.
Zodiacal light is only visible at certain times and places because this is when the dust band is nearly vertical at sunrise, so the thicker air viewed along the horizon doesn’t block the light from the dust. Its observation has been noted in Islamic texts, as Muslims needed to recognise the phenomenon so as not to begin morning prayers at the wrong time.