I am trying to figure out the position of sun with respect to moon on a full moon day.

Here's an image from certain wiki which I do not find convincing. enter image description here1

If the sun rays point as shown in the image and the earth stands between the moon and sun on Full moon's day, I dont see any reason why the moon should be shining in its full glory.

Similarly when the moon is directly in between earth and sun, it should have maximum brightness but the image shows it as the new moon.

In fact, I cannot deduce how at all can moon receive light across the entire sphere at any given angle from the sun.

Putting it specifically, what would the position of sun w.r.t to earth and moon on a full moon day ?

  • 3
    $\begingroup$ Ouch! That's the most horrible illustration I've seen! And the source is "Monn's Phases". Just confusing people. Here are a couple of actual photos of Earth and the Moon together. It is intuitively easy to understand that the Earth will not always shadow the full Moon. $\endgroup$
    – LocalFluff
    Dec 28, 2014 at 15:56
  • $\begingroup$ Uhhh... Should not the moon in the diagram look exactly the same as it moves around the earth? For example, the left side of the moon should never have any illumination! $\endgroup$
    – DJohnM
    Dec 29, 2014 at 0:42

2 Answers 2


The orbits are not all in exactly the same plane, that is why we do not have eclipses every month. With the orbits at a slight skew it is possible to have the geometry very near to that in your diagram without the Earth blocking the Sun.

Lunar eclipses, the Moon passing through the Earth's shadow which is what your post is about, do occur relatively frequently compared to Solar eclipses because the Earth is bigger than the Moon.

At New Moon the lit side of the Moon is facing away from the Earth and so we do not see it.

You will find a fairly good explanation, and a better diagram, of all this here


I found this little video from youtube as pretty good explanation for my question.



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