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Here Comes the Sun
Question by Ethan Gelber

The Question:

We all know from too many science fiction movies and greenhouse effect warnings that only some of the sun's energy reaches the surface of the earth and that even less of it is actually absorbed by the earth.

What percent of the sun's strength is believed to be retained by the earth, and what is the part that is reflected back called?

The Answer:

The fraction of sun's light (its energy) reflected back from the surface of the earth is called the albedo. Usually expressed as a percentage, it is also a measure of a planet's energy balance. (There are two different kinds of albedo; we are focusing on the bond albedo here, not the normal albedo.)

Latest measurements place the earth's albedo at 33 percent. Thus, one-third of the sun's energy does not influence the earth's environment. By contrast, the moon's albedo is about 12 percent and the albedo of cloud-covered Venus is about 76 percent.

The Winners:

Our winners this week are: Steve Yates, Ena Lynne Wilson, and Jason McCurdy. Kyle Brock gets a special thumbs-up here for guessing the right reflected percentage, but only after trying every whole number value between 5 and 35 percent. Persistence does pay!

THANKS for your contributions!