Here's why:

* Lunar phases: The Moon's phases are caused by the changing angle of sunlight hitting the Moon as it orbits Earth. We see different amounts of the sunlit side of the Moon from Earth.

* Rotation: The Moon rotates on its axis at the same rate it orbits Earth. This means the same side of the Moon always faces us, but it doesn't mean that side is always bathed in sunlight.

What *does* have constant sunlight?

The Moon's poles are always in either constant sunlight or constant darkness (depending on the crater they are in). These areas are of interest to scientists because they might contain water ice.