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The Sciences

Discover Data: A Lunar Mirror on Earthly Climate

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by Hannah Hoag

The amount of sunlight our planet bounces back to space, a key factor affecting global temperature, has proved difficult to measure accurately. Astronomer Phil Goode of the New Jersey Institute of Technology has a simple solution: Look at the amount of earthshine illuminating the night side of the crescent moon. Goode and his colleagues measured the earthshine over 270 days using the solar telescope at Big Bear Observatory in southern California. They found that Earth is roughly 10 percent more reflective than average in April and May, a disparity almost twice as great as NASA's computer models predicted. Apparently, our planet is cloudier than expected during those months. The observations also suggest that Earth's reflectivity drops by 2.5 percent during times when the sun is active. Goode hopes to place eight robotic telescopes around the world so he can monitor the moon continuously and watch for long-term trends: "We want to see what happens over an 11-year solar cycle."

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Graphic by Matt Zang

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