* New Moon: This is when the moon is positioned between the Earth and the Sun. The sunlit side of the moon is facing away from us, so we can't see it.

* During the day: Even though the moon is up during the day, it's often too faint to be seen against the brightness of the sun.

* Hidden by clouds: Obviously, you can't see the moon if it's behind clouds.

So, while the moon is always on its orbit, you can't see it when it's in these specific positions.