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Eyes on the Sky
with David Fuller
Earthshine Moon

Earthshine is the coolest thing

April 23, 2012

Okay, I'm not a huge lunar observing fan, though I take my views of craters every so often. And yet there is just something about earthshine I find fascinating.  And then it hit me the other day as I was writing my script for this week's video.  When you see earthshine, you're seeing sunlight that is both immediate, and delayed - simultaneously.  

The sunlight bouncing off the Moon's lit crescent side takes 1.3 seconds to reach your eye (~240,000 miles / 186,000 miles per second = 1.3).  But the dark side of the moon (can't help it - I like Pink Floyd) where the earthshine is seen during early crescent phases, has traveled a slightly longer path.  It's gone the same distance, to Earth, but then it's bounced back to the Moon (from Earth's surface / clouds / etc.), then back again off the dark side to your eye.  So the same sunlight arrives at your eye 2.6 seconds or so later than the "brighter side" light did.

Anyway, when I saw the phenomenon tonight that I'd talked about in this week's video (Eyes on the Sky: April 23 thru April 29) - and it was clear tonight! - I captured some actual video of earthshine and put this together.  I even managed to capture it in some different exposure settings, but of course the very best way to see earthshine?  Your own eye.  It can handle the contrast difference better than just about any camera.  Try spotting it with binoculars or any small telescope.  

It really IS cool to see.

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