The amount of sunshine reaching the surface of the earth has decreased drastically in recent decades. This has important implications for the magnitude and direction of climatic change. A question of interest is, how do we know about the decrease. There are various means of measuring it, but one of the more interesting is by using earthshine.
What in the world is earthshine? Actually, it's nothing in the
world. Instead, it's the reflection from the moon of the reflection of the
sun's light from the earth. Confused enough? When the moon is low on the horizon
before dawn or after sunset, most of our view is of its dark side. By looking
carefully, you'll see that the darkness is not absolute; it glows faintly. This dim
light is from sunlight reflected from earth—the earthshine we're talking
about. By tracking the brightness of the earthshine through time, we can estimate
changes in how much light reaches the earth's surface. That crescent moon hanging
over the Southwestern desert scene is much more than an inspiration for poets!
Contributor: Arthur H. Harris, Laboratory for Environmental Biology, Centennial Museum, University of Texas at El Paso.
Desert Diary is a joint production of the Centennial Museum and KTEP National Public Radio at the University of Texas at El Paso.