Did you see the moon last night! Northern spring is a great time to look at the moon as you easily see the phenomena of earthshine. The bright crescent of the moon is reflected sunlight. But the dark part of the moon, the part that should be in shadow, is very bright over the next few nights. This is lit up by light reflecting from Earth back onto the moon in a phenomena known as earthshine. It is also known as the Moon’s ashen glow or as the old Moon in the new Moon’s arms.

We’ve known about this for a long time. Leonardo da Vinci sketched the crescent Moon with earthshine as part of his Codex Leicester, written between 1506 and 1510. Recently it has taken on a new level of importance in the study of global warming. The amount of earthshine is a proxy for the amount of the earth’s reflectance, known as its albedo. And this is directly related to the amount of clouds in the atmosphere. So the scientists at big bear solar observatory have an ongoing project measuring the amount of earthshine each night.

So have a look up tonight and see if you can spot earthshine.

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