When you look at a crescent moon shortly after sunset or before sunrise, you can sometimes see not only the bright crescent of the moon, but also the rest of the moon as a dark disc. That pale glow on the unlit part of a crescent moon is light reflected from Earth. It’s called “earthshine.”
What’s happening in the sky tonight: Daily sky charts and more
Photo credit: carolune
To understand earthshine, remember that the moon is globe, just as Earth is, and that the globe of the moon is always half-illuminated by sunlight. When we see a crescent moon in the west after sunset, or in the east before dawn, we’re seeing just a sliver of the moon’s lighted half.
Now think about seeing a full moon from Earth’s surface. Bright moonlight can illuminate an earthly landscape on nights when the moon is full.
Likewise, whenever we see a crescent moon, a nearly full Earth appears in the moon’s night sky. The full Earth illuminates the lunar landscape. And that is earthshine. It’s light from the nearly full Earth shining on the moon.
So next time you see a crescent moon, expand your thinking – to include the Earth under your feet. See the glow on the unlit portion of the moon for what it really is – sunlight reflected from the nearly full Earth shining in the moon’s sky.
Moon with earthshine and planet Venus. Photo credit: fdecomite
It’s absolutely stunning tonight on the north coast of California. The crescent is nearly horizontal and the earthshine is very pronounced. Venus is huge!
This makes it obvious that the moon is a ball. Why the hell didnt see that our anchestors thousands of years?
Thanks, I love this pictures
So worth the time and the read! Thank you (:-)
Beautiful! But I dont understand. Light reflected from earth? How is that possible? Why dont we see it like that all the time, just sometimes?
Eva,
Earthshine on the moon is like being outside on a night when there’s a full moon in Earth’s sky. You know how when there’s a full moon, moonlight illuminates the landscape all around you? This is the same phenomenon … only now it’s a “full Earth” illuminating the lunar landscape.
The trick is: when we see a crescent moon from Earth, any moon beings would see a nearly full Earth in their sky.
I hope this helps!
Deborah
…Just want to add something. Maybe my thinking sometimes is to slow. I have read the article, but I still dont get how that is possible….
But anyway. Love earthand sky.com and all this interesting facts!
Greetings from Norway! :)
Visualizing things in the sky in three dimensions is really hard! Psychological studies have shown it is one of the hardest things to think about.
Greetings to you Eva from the U.S.!
Deborah
I’m a prolific amateur astronomer with my own observatory at a dark sky site as well as my own setup at home. Besides my outreach duties as a JPL Solar System Ambassador I am nearly always out under the newest new Moon when the Earthshine is at maximum. This month I was fortunate to be on AstroCation at my friend’s place in New Mexico at 7,100′ where the rarefied dark air allows such phenomena to emit subtle to spectacular light shows. The hues of the pale blue Earthshine differ from galactic shadows cast by the Milky Way.
Cheers,
max
Hi Max, that sounds very beautiful. If you have photos, I know our Facebook community would love to see them … http://www.Facebook.com/Earthsky
Thanks for dropping by!
Deborah