Astronomy Picture of the Day

Explanation: Although you've surely seen it, you might not have noticed it. During a cloudless twilight, just before sunrise or after sunset, part of the atmosphere above the horizon appears slightly off-colour, slightly pink or orange. Called the Belt of Venus, this off-colour band between the dark eclipsed sky and the blue sky can be seen in nearly every direction including that opposite the Sun. Straight above, blue sky is normal sunlight reflecting off the atmosphere. In the Belt of Venus, however, the atmosphere reflects light from the setting (or rising) Sun which appears more red. Below the Belt of Venus, the atmosphere appears more dark because no sunlight reaches it. The Belt of Venus can be seen from any location with a clear horizon. Pictured above last month over Mercedes, Argentina, a panoramic vista featuring the Belt of Venus was digitally stitched together from 16 smaller images. The belt is frequently caught by accident in other photographs.