The ghostly glow of comet dust brightens an October dawn.
This is the zodiacal light, as it appeared two mornings ago in the pre-dawn sky from my backyard in southern Alberta. This tapering glow angled up from the horizon is best spotted in the eastern sky on clear and moonless autumn mornings, like this one.
What you are seeing is sunlight reflected off dust left by passing comets in the inner solar system. So while this glow looks like it might originate in our atmosphere it really comes from dust out in interplanetary space.
This subtle glow, often called the “false dawn,” appears in the hour or so before the true dawn begins to brighten the sky too much (its purple light is just starting to light the horizon here).
Also visible here: Sirius at far right, Jupiter above centre, the Beehive star cluster below Jupiter, and Leo rising embedded in the zodiacal light, with Mars just above Regulus, Leo’s brightest star. The planets lie along the zodiacal light because the dust that causes it also lies in the same plane as the orbits of the planets, the ecliptic plane.
I shot this with a 14mm lens for a stack of four 2-minute tracked exposures, but with the horizon coming from just one of the exposures to minimize blurring from the moving camera slowly following the sky.
– Alan, October 10, 2013 / © 2013 Alan Dyer
The Amazing Sky 