Astronomy Picture of the Day

Explanation: Where is the Sun when you see a rainbow? Behind you, of course. But you can see both a rainbow and the Sun (far right) side by side in this graceful panorama recorded on July 28. The cloudy sunset view covers a full 360 degrees around the horizon, composed using 20 individual images taken from an observatory on the outskirts of Potsdam, Germany. The rainbow itself is produced by sunlight internally reflected in rain drops from the direction opposite the Sun back toward the observer. As the sunlight passes through the drops, from air to water and back to air again, longer wavelengths (redder colours) are refracted or bent less than shorter wavelengths (bluer colours), separating the sunlight into the colours of the rainbow. This sharp picture captures the full, bright, primary rainbow arc as well as more subtle effects. You can see a partial, dimmer, secondary rainbow arc above and left of the primary, and faint arcs just inside the primary rainbow called supernumerary rainbows.