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What is the term for light from the dark part of the moon facing earth

  1. Apr 25, 2007 #1
    What is the light that you are seeing when you look at a crescent moon but you can still see the dark side faintly?

    thanks
     
  2. jcsd
  3. Apr 25, 2007 #2

    mezarashi

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    The light you see from the noon at any time is reflected light from the sun. The shadow you see on the moon that causes it to become crescent is the shadow of the earth. You will generally be able to see areas bordering the shadow, but because there isn't much in space to reflect around light, it would be hard to see areas beneath the shadow.

    Would you have a specific photo of what you mention?
     
  4. Apr 25, 2007 #3

    russ_watters

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    When the moon is a thin crescent, the Earth is near "full" as seen from the moon, reflecting a lot of light toward the moon, which in turn reflects some back to earth, making the "dark" part of the moon visible.
     
  5. Apr 25, 2007 #4

    mezarashi

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    Ah, that's interesting. I've never noticed this myself. Alright, when's the next crescent moon.
     
  6. Apr 25, 2007 #5
    Thats what I figured myself. You just missed the best one I have seen yet last tuesday or thursday. I forgot which day.
     
  7. Apr 25, 2007 #6

    russ_watters

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    During the spring in the northern hemisphere, the angle of the ecliptic puts the moon directly above the setting sun, making it more visible for longer in its crescent phase.

    I've been trying to capture this phenomena myself: http://www.russsscope.net/images/moon1.jpg
     
  8. Apr 26, 2007 #7
    [​IMG]

    I'm sure pictures dont do it justice.... I wonder what it would be like to see the entire planet..... all 7 billion humans..... the place where all of our history and present happens... in one blue circle :)
     
  9. Apr 26, 2007 #8

    Chronos

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    Earthshine, as Russ already noted, is what illuminates the unsunlit surface of the moon. The earth is phenomenally bright viewed from the surface of the moon. The brightness [albedo] varies depending on atmospheric conditions on earth - clouds are more reflective in the visible spectrum than the surface of the earth. For another pic:

    http://apod.nasa.gov/apod/ap020419.html
     
  10. Apr 26, 2007 #9
    I just noticed this last summer. I'm glad it's not light pollution.
     
  11. Apr 26, 2007 #10
    I have heard of people taking spectra of India by observing the moon!
     
  12. May 2, 2007 #11
    Hmmm. . . I don't think this is quite right. The "shadow" you see on the moon that causes it to be a crescent is not the shadow of the Earth. It is simply the side of the Moon facing away from the Sun. It is the night-time side of the Moon.

    The only time a shadow of the Earth causes any darkness on the Moon would be during a lunar eclipse, which happens only a couple of times a year.
     
  13. May 3, 2007 #12

    russ_watters

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    You're right, smithpa9 - I missed that when I first went through the thread. Good catch.
     
  14. May 3, 2007 #13

    DaveC426913

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    And even then, Earth's shadow is so broad doesn't even resemble a shadow at all. The gradient from light to shadow spans the whole moon's face, making it simply look like the moon is somewhat darker altogether with one limb even darker.

    It is quite possible to not realize you're seeing a lunar eclipse at all.
     
  15. May 3, 2007 #14

    russ_watters

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    That isn't true, Dave. When the moon is eclipsed, it is in the umbra of the shadow - receiving no direct light. It appears red because of light scattered towards it by the atmosphere. http://www.hermit.org/Eclipse/why_lunar.html
     
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