The twice reflected Moon light

By Phil Plait | November 19, 2011 7:22 am

American astronaut Ron Garan may be the single best promoter of space exploration we have today, if only because of his breathtaking photographs of the Earth from space. In July 2011, as he orbited our planet in the International Space Station, he took this gorgeous shot of the crescent Moon, setting over the Earth’s silhouetted limb:

[Click to enlunenate.]

This shows no fewer than three of my favorite optical effects! First, the colors of the sunset are due to the Earth’s air, which preferentially scatters away bluer light, leaving just the orange and red colors from the Sun to get through.

Second, the Moon is squashed! You can see it’s not perfectly round as it usually looks; again, that’s due to Earth’s air. It acts like a lens, bending the Moon’s light. Nearer the Earth’s limb, you’re looking through more air, so the effect is larger, making the moon look not just squashed, but squashed unevenly: the top part is rounder than the bottom. I explain in this in detail using a different picture of moonset from space.

And third, of course, is that you can see the dark part of the Moon, gently illuminated. This is called Earthshine, or, more poetically, "the old Moon in the new moon’s arms" (soon to be a twilight sequel). When the Moon is new, it’s more or less between us and the Sun. if you were standing on the Moon, you’d see the Sun on one side of the sky and the Earth on the other. To you, the Earth would be full! The full Moon is bright enough to cast shadows here on Earth, and in the Moon’s sky The Earth is much brighter and bigger. It’s actually bright enough to light up the part of the Moon not lit by the Sun, and that’s what you’re seeing.

Think about the journeys of all those photons that make up this picture: some came straight from the Sun, a trip of 150 million kilometers, only to be scattered away at the last moment; some redder ones made it all the way through; some hit the moon and came toward us but were bent a bit by Earth’s air, distorting the Moon’s face; and others still came from the Sun, hit us, went to the Moon, hit there, came back to us, finally making it into the lens of a camera held by a man hanging in the cupola of a football-field-sized metal can orbiting 350 kilometers above our planet at 30,000 kilometers per hour.

To some people, this might just be a pretty picture of the Moon. But when you look past that, you see it’s also a portrait of the incredible subtlety and complexity of the way the Universe works. And that’s one of the things I love about astronomy: what you get out of it depends on how much you want to know. There’s always more.


Related posts:

Crescent Moonset seen from space
The Moon is flat!
The Moon, waxing poetic
A new day, from space

CATEGORIZED UNDER: Astronomy, Cool stuff, Pretty pictures
MORE ABOUT: Earthshine, ISS, Moon, Ron Garan

Comments (16)

Links to this Post

  1. Aim for the Moon… | createwhatyouwant | November 19, 2011
  1. Cindy

    I always love pointing out Earthshine to my kids and anybody else who happens to be nearby.

  2. Randy A.

    Fantastic photo! Thanks for sharing it with us!

  3. It would be awesome to see a full Jupiter from Europa or a full Saturn from Enceladus (lol, Firefox spell check wants Enceladus to be Enchiladas) Those would definitely cast shadows.

  4. I like how you can also see the shapes of clouds in the Earth’s atmosphere. Just so much stuff to look at in that single photo. :)

  5. john

    Have there been any phographs of the Earth taken from inside its shadow, such as you would see from the Moon during a lunar eclipse?

  6. Do they make “Earthshine” on the moon?

  7. If no one watches that show I am going to be so bummed :-P

  8. Ignignokt

    @#5 Alex: Of course we do, and it is far superior to your puny earth Moonshine, though Moon Moonshine is also called Moonshine, for the Moon is advanced beyond anything your non-Moon brain can possible comprehend. Some would say that the earth is our Moon, but that would belittle our Moon which is…the Moon. I don’t know if you can understand that, but if you could, I’m sure you’d really want some Moon Moonshine right now, which is unfortunate, because we’re going to drink all of it, for we are awesome.

  9. Great photo – thankyou Ron Garan & the BA for the great write up here. :-)

    Off topic, sorry (don’t know how else to let him know) :

    @Sam H. here’s a comment (#47) and suggestion for your SF novel idea set around 70 Ophiuchi mentioned on the old “unreal picture” thread :

    http://blogs.discovermagazine.com/badastronomy/2011/11/17/an-unreal-picture-of-sunset-at-the-north-pole/comment-page-1/#comment-442896

    Hope you see this & its useful / interesting for ya. :-)

  10. Chris

    Those last two paragraphs are positively Sagan-esque. :D

  11. Paolo Nespoli was another great photographer who went to the ISS; I loved all the photos he took up there.

  12. jwoodguy

    Thanks for continually making my desktop wallpaper more stunning!

  13. @12. Matt McIrvin : Paolo Nespoli was another great photographer who went to the ISS; I loved all the photos he took up there.

    Seconded by me. :-)

    PS. Click on my name for the BA blog items tagged ‘Paolo Nespoli’ too – the last one there (‘Squishy moonrise seen from space!’ posted January 21st, 2011 11:30 AM.) has a link to Paolo Nespoli’s flickr page.

  14. Sweetgazer1

    Phil, your descriptions are always so rich and enlightening, a perfect match to Ron’s pictures. I´m a fan too of Paolo Nespoli’s photos as well as of those by Mike Fossum (presently on board the ISS), Doug Wheelock and Soichi Noguchi.

  15. Slim

    Such a thin crescent, it’s almost like that painting you said couldn’t be a photo the other day. By the way, that’s how I knew it was just a painting– I was left asking, “Where’s the Earthshine?”

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