The moon's shape as seen from Earth changes throughout the month, going through different phases. These phases are caused by the changing angles of sunlight reflecting off the moon's surface.

However, the actual shape of the moon itself is a sphere.

Here's why it appears to change shape:

* We only see a portion of the moon's illuminated surface. The sun illuminates half of the moon at any given time, but we only see the part that is facing both the sun and Earth.

* The moon orbits the Earth. As the moon orbits, the angle of the sun's light hitting the moon changes, causing the illuminated portion we see to shift. This creates the phases of the moon, from new moon (invisible) to full moon (fully illuminated).