The Moon goes through phases throughout the month because of its position relative to the Earth and the Sun. The phases of the Moon are determined by the interplay between these three celestial bodies.
The Moon itself does not emit light but reflects sunlight. As it orbits the Earth, different portions of the Moon's surface are illuminated by the Sun, resulting in the various phases that we observe.
Here's a simplified explanation of the lunar phases:
New Moon: During a new moon, the Moon is positioned between the Earth and the Sun. The side of the Moon facing Earth is not lit by sunlight, making it appear dark or invisible from our perspective.
Waxing Crescent: As the Moon continues its orbit, a small portion of the Moon becomes visible as a crescent shape. This phase is known as the waxing crescent.
First Quarter: When half of the Moon's visible side is illuminated, it is referred to as the first quarter. At this stage, we see half of the Moon's disk illuminated, resembling a "half moon."
Waxing Gibbous: The illumination of the Moon increases further, resulting in a phase called waxing gibbous. The Moon appears more than half lit but is not yet a full moon.
Full Moon: When the Moon is directly opposite the Sun, with the Earth between them, we observe a full moon. The entire side of the Moon facing Earth is illuminated, giving it a circular shape.
Waning Gibbous: After the full moon, the illuminated portion of the Moon gradually decreases. This phase is known as waning gibbous. It appears as a partially lit disk, but less than a full moon.
Third Quarter: When half of the Moon's visible side is again illuminated, it is referred to as the third quarter. It is similar to the first quarter phase but appears on the opposite side of the Moon.
Waning Crescent: In the final stages of the lunar cycle, only a small crescent portion of the Moon is visible. This phase is called the waning crescent.
The cycle then repeats with a new moon, completing the lunar month, which lasts about 29.5 days.
The changing appearance of the Moon's phases is a result of the relative positions of the Earth, Moon, and Sun, as well as the geometry of the sunlight falling on the Moon's surface.