As the Moon orbits Earth, different parts of it are illuminated by the Sun, causing its appearance to change. This phenomenon is called the lunar phases, and it results in the Moon going through a series of distinct shapes or phases as seen from Earth.

The cycle of lunar phases begins with a New Moon, when the Moon is positioned between Earth and the Sun. During this phase, the side of the Moon facing Earth is not illuminated, and it appears as a dark circle in the sky.

As the Moon continues its orbit, it gradually moves away from the Sun's direct line of sight. This causes more of the Moon's surface to become visible, resulting in the Waxing Crescent phase. The term "waxing" refers to the gradual increase in the illuminated portion of the Moon.

As the Moon continues to orbit, it reaches the First Quarter (also called the Waxing Gibbous) phase. At this point, exactly half of the Moon is illuminated, and it appears as a semi-circle in the sky.

Continuing further along its orbit, the Moon reaches the Full Moon phase. This occurs when the Moon is positioned opposite the Sun in the sky, with the Earth in between. During this phase, the entire side of the Moon facing Earth is illuminated, and it appears as a complete, bright circle.

After the Full Moon, the Moon begins to move away from the Sun again. This leads to a gradual decrease in the illuminated portion of the Moon, resulting in the Waning Gibbous phase.

As the Moon continues to move around Earth, it eventually reaches the Third Quarter (also called the Waning Crescent) phase. At this point, half of the Moon is illuminated again, but this time it's the opposite side compared to the First Quarter phase.

Finally, the Moon completes its orbit and returns to the New Moon phase, starting the cycle over again.

So, as the Moon orbits Earth, the changing positions of the Moon relative to the Sun and Earth give rise to the different lunar phases that we observe in the sky.