The appearance of the Moon changes throughout the lunar cycle due to the changing angles of the Sun, Earth, and Moon. As the Moon orbits the Earth, it reflects sunlight back to us. The amount of sunlight that we see reflected from the Moon depends on the angle at which the sunlight is striking the Moon.

During a full moon, the Sun, Earth, and Moon are in a straight line, with the Earth in the middle. This means that the entire face of the Moon is reflecting sunlight back to us, and we see a fully illuminated Moon.

As the Moon orbits the Earth, it begins to move away from this straight line. The angle at which the sunlight is striking the Moon becomes smaller, and we see less of the Moon's face illuminated. This is why the Moon appears to shrink from a full moon to a crescent moon.

At a new moon, the Moon is on the same side of the Earth as the Sun. This means that the side of the Moon that is facing us is not illuminated by sunlight. We cannot see the Moon at all during a new moon.

The lunar cycle repeats itself about every 29.5 days. This is the amount of time it takes for the Moon to complete one orbit around the Earth.