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We can see the moon in the night because it reflects sunlight. But the light is incident on the opposite side of moon with respect to the observer in the night.

In this case, how does the moon reflect light?

I am not sure if I have articulated my question correctly.

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I don't have a slightest idea what you are talking about. Look at this picture: en.wikipedia.org/wiki/File:Moon_phases_en.jpg What is your problem with it? –  Marek Mar 20 '11 at 17:32
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@marek the problem with those diagrams is by showing the moon so close to the earth they make it look like the moon is in the earth's shadow half the time –  Martin Beckett Mar 20 '11 at 22:11
    
@Martin: that is not really a problem as long as one possesses at least a tiny amount of rational thinking. This picture just shows the correspondence between lunar phases and relative position of objects. Nothing less or more. –  Marek Mar 20 '11 at 22:29
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I guess the essence of the question boils down to this: "If Earth is between Moon and Sun during full moon, how can sunlight get passed Earth to light up the Moon?" –  Qmechanic Mar 21 '11 at 11:20
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4 Answers

up vote 12 down vote accepted

The problem with most of the earth-moon pictures is that they show the Earth and moon very close together - which suggests that the moon is in the earth's shadow for almost half of the time.

So in the picture linked to above - it looks like a full moon should be dark.

enter image description here

The real picture is more like this

enter image description here

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Very nice! I had not grasped the true scale myself, to be honest. –  Andrew Mar 21 '11 at 2:07
    
The inclination of the moons orbit around earth also often prevents that the moon will to move into earths shadow. –  fibonatic Aug 9 '13 at 1:22
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Although this question is answered, I will say this: the orbital plane of moon is not in the same orbital plane of earth, there is about 5 degrees of inclination.

Example, if earth and sun was in the floor of a room, then the moon is on the opposite of sun, but raised from the floor . Now since sun is larger than the earth, the umbra of the shadow cone is diminishing behing the earth, see here: http://celestrak.com/columns/v03n01/fig-1.gif

Usually the moon is also outside the Pen-Umbra zone. That is why the mon gets illuminated, even being at the opposite side of sun (looking from top). Sometimes however, the moon, while in the opposite side of sun wrt earth, stays in the ascending or descending node, that is called a lunar eclipse.

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The surface of the moon is rough rather than shiny so it scatters light in all directions.

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This answer is less clear than the question. –  iamnotmaynard Feb 7 at 21:20
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I think Marek's comment is the correct answer. I will rephrase it here slightly:

I think one of your assumptions is faulty. Look at this picture. Do you still have a question, after seeing this picture?

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Thanks for the pic . What I was thinking is , during the Full moon time in the pic , the earth may block out all the sun light going to the moon ...since earth is larger than moon. –  vinoth Mar 20 '11 at 17:45
    
There are some good pictures here, relevant to that thought: en.wikipedia.org/wiki/Lunar_eclipse –  Andrew Mar 20 '11 at 17:53
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Dear user2678, this invisible Moon during full moon can happen, indeed, and it is called lunar eclipse, see en.wikipedia.org/wiki/Lunar_eclipse - However, it doesn't occur during every full moon because the planes in which Earth orbits around the Sun, and Moon around the Earth, don't quite coincide, so the 3 celestial bodies are not exactly in line, even during a typical full moon. –  Luboš Motl Mar 20 '11 at 18:08
    
Why don't you edit the picture into your answer? Oh I see, it's already in the other answer. –  Carl Brannen Mar 21 '11 at 4:00
    
It's already in the other polite, constructive answer ;) –  Andrew Mar 21 '11 at 12:41
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protected by Qmechanic Oct 29 '13 at 20:16

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