Moon phases are caused due to the relative positioning of the Earth, Moon, and Sun. As the Moon orbits around the Earth and the Earth orbits around the Sun, different portions of the Moon are illuminated by the Sun. The amount of illuminated portion that is visible from Earth changes throughout the month, resulting in the different moon phases.

To understand why we see different moon phases, imagine standing on the Earth's surface and looking towards the Moon. As the Moon orbits around the Earth, its position relative to the Sun and Earth changes.

1. Full Moon:

During the full moon phase, the Moon is located directly opposite the Sun from the perspective of an observer on Earth. This means that the entire face of the Moon that is facing Earth is illuminated by sunlight. The Moon appears as a complete, bright disk in the night sky.

2. New Moon:

During the new moon phase, the Moon is located between the Earth and the Sun. In this configuration, the side of the Moon that is facing Earth is not illuminated by sunlight. As a result, the Moon is not visible from Earth.

3. Waxing and Waning Moons:

Between the full and new moon phases, we observe waxing and waning moon phases. During the waxing phase, the illuminated portion of the Moon gradually increases as it moves from the new moon towards the full moon. During the waning phase, the illuminated portion of the Moon decreases as it moves from the full moon towards the new moon.

The moon phases repeat in a regular cycle that lasts for approximately 29.5 days, which is the time it takes for the Moon to complete one orbit around the Earth.