How does the moon's position change?
The Moon's position changes due to Gravity. The Moon revolves around earth. However, due to earth's axis we see the moon many different positions during the year, that we would not normally see. This is also responsible for eclipses. Which can only be seen on certain parts of earth, also because of the axis.
As the earth spins on it's axis, the moon appears to move across the night sky against a backdrop of stars.
The next day, the same thing happens but the moon follows a slightly different path. This is because the moon is also moving around the earth, in an orbit.
As the moon orbits the earth it presents a different angle to the sun. This causes the reflection to shine from a different edge, causing the phases of the moon.
Inevitably there will be a time when the moon gets betwen the sun and the earth and causes a shadow to pass over the earth's surface. This is an eclipse. Each time a shadow is cast, it tracks across a different part of the earth and only from this path, can a full eclipse be seen.