Photo: Night lights

April 5, 2001

This composite of satellite images shows how the Earth looks after dark. Man-made lights brighten urban areas. The military satellite network used to make this image was originally designed to aid aircraft navigation at night by picking up moonlight reflecting off clouds. Air Force observers discovered that, on moonless nights, the satellites could 'see' city lights.

For a detailed view of this image on the Web, go to:

antwrp.gsfc.nasa.gov/ apod/image/0011/ earthlights_dmsp_big.jpg