The moon does not physically change its shape. As it orbits the Earth, it goes through phases, and sunlight and shadows create a slightly different look each night. It takes about one month for the moon to completely cycle through its phases.
As with all planets and other lunar bodies in the solar system, the moon doesn't emit its own light; it reflects sunlight. When a full moon is observed, it is positioned on the opposite side of the Earth to the sun, and when a new moon is experienced, the moon and the sun are on the same side of the Earth. From the sun's point of view, the moon is always full since there are no obstructions to create shadows.
During a lunar eclipse, the moon will go through all its phases in a matter of hours. A lunar eclipse occurs as the moon slowly enters, traverses and leaves the Earth's shadow. The moon often takes on a red hue, nicknamed a blood moon, during an eclipse as a small portion of sunlight wraps around the Earth and reflects off the moon's surface. When the moon is precisely positioned between the Earth and the sun, a solar eclipse occurs, which is sometimes partial or total.