What causes the moon to look different each night?

Answer 1

Every night when the earth is rotating, in certain positions, clouds will be covering some of the moon. As the moon circles the Earth, the shape of the moon appears to change; this is because different amounts of the illuminated part of the moon are facing us.
The phases of the Moon depend on its position in relation to the sun and Earth. As the Moon makes its way around the Earth, we see the bright parts of the Moon's surface at different angles. These are called "phases" of the Moon.
We only see the part of the moon that is illuminated by the sun, and since the sun, the moon, and the Earth are constantly in motion and changing their relative positions toward each other, different amounts of illuminated surface of the moon are exhibited to any given viewer on Earth.
The Sun, Moon, and Earth are at different angles with respect to each other. The Earth's orbit around the Sun is about 365.25 days, the Earth's rotation about its own axis relative to the Sun is about 24 hours (that's an average value - it varies) and the Moon's orbit around the Earth is about 29.57 days (again an average, because of the multiple dynamics involved.

The moon is always a sphere, What you see, however, is the part the sun shines on and that we can see. Normally, the lunar calendar starts with the new moon when the moon Earth and Sun are reasonably lined up. This is the New Moon. Soon after that we get a waxing crescent to a gibbous moon that grows to Full Moon. That occurs 14.57 days later, following that. Following that there is a gibbous moon that transitions in to a waning crescent moon that leads to a new moon and the cycle starts all over again, again in 14.57 days.

Once in a while, the orbit of the Moon lies close to the same plane the Earth rotates around the sun. This causes lunar eclipses, where the shadow of the Earth lands on the Moon, or it causes Solar eclipses, where the shadow of the moon lands on the Earth.

Now the moon that we see is the part with light on it, that we are able to see. Since the moon's revolution around its axis is also synchronized to its orbit around the Earth, the same face of the moon will always be presented to the Earth. This is why the moon does not appear to turn.
It moves relative to the Earth and Sun. Each night it is in a slightly different part of the sky and the angle between the Sun, Moon and Earth changes.

So, different proportions of the sunlit hemisphere are seen from a particular location on Earth.
It is different every night, it depends on how much sunlight is falling on the side of the moon we see. When we see full moon the side we see is in full sunlight. When we see a small crescent moon it is mostly night-time on the side we see.
The moon always remains the same shape. But on its monthly journey around the earth, the sun appears to light up different portions of it. When the moon is between the earth and sun, all we see is the portion which has fallen into shadow. This is the "new" moon. As the moon changes position, it waxes, or grows more lit. About a week after the new moon half the surface is lit by the sun, making the moon appear to be half full. A week after that (a fortnight) the moon is behind the earth, and it appears fully illuminated by the sun, and very bright. After its fullest extent the moon begins to wane, until two weeks later it reaches the new moon state again.
The Moon is moving round the Earth. This causes us to see different amounts

of the sunlit portion of the Moon.