What are the positions of the sun the moon and earth during a full moon?

Answer 1

When the moon is full, the full of the face of the moon that is facing earth is lit by the sun. The only way this can happen is if the earth is between the sun and the moon. We need the sun "behind us" to allow the sun to light up all of the moon's face so it can appear full.

Answer 2

The position of the moon from the sun and earth can differ. The sun and earth are in two different places, so from the sun it would be in different from the earth. From the earth it would be in different places every month. Every month there is a new moon. __________________ The questioner may be asking about the lunar phases and/or the synodic cycle. Interesting things happen when we observe bodies [the moon] that are orbiting something [the earth], especially when that 'something' [the earth] is itself orbiting something else [the sun]. When we observe the moon from earth and we consider its position in relation to the sun, we are observing a particular lunar phase. When we measure the time between a particular lunar phase and the next time that the moon will be in that exact same lunar phase, we are talking about the synodic cycle of the moon. Obviously enough the earth orbits the sun, and at the same time the moon orbits the earth. So we are really NOT observing the moon's true, absolute orbit around the earth-- we are looking to see how long it takes from one particular match-up of the moon and sun until the next match-up exactly like the first. The orbit and the 'match-up'... aren't they the same? No, they are not. While the moon is on its month-long journey around us, the earth moves roughly 1/12 of its way through its own orbit. As a result, since the lunar phases are related to the synodic cycle, the moon has to travel a little farther than 360 degrees in order to line up the same way in relation to the sun. Imagine the earth at 6 o'clock and the sun at the center of the clock. The New Moon would be when the moon is exactly between the earth and sun. Now imagine the earth one month later at 3 o'clock*. If the moon covers 360 degrees only, it will be pointing straight up above the earth, as it is with earth at 6 o'clock. In order for the New Moon to occur, the moon has to continue in its orbit until it matches up with the sun in the same way as at 6! The moon has to again be directly between the earth and sun. This repeats the moon phase, but the moon moves MORE than one full rotation. Matching up with the sun is a key idea when considering the moon's synodic cycles. *The clock analogy is only a simple illustration and is not accurate in terms of measurement. The earth doesn't move quite that much in one month, but the principle applies. Both orbits discussed above are anticlockwise when observed from high in the north sky.