Today’s instalment on the countdown to #observethemoon.

Different countries see different phases of the Moon on the same day.

Everyone sees the same phases of the Moon, but we who live south of the equator who face North to see the Moon when it is high in the sky will see the Moon upside down from our Northern friends so that the reverse side of the Moon is lit.

The Moon does not rotate.

The Moon does in face spin on its axis. It completes a rotation once every 27.3 days.

The confusion is caused due to the fact that it also takes the same period of time to orbit the Earth, so that it keeps the same side facing us.

The Moon takes 27 d 7 h 43 min to revolve around the Earth, considering the turning with respect to background stars (sidereal revolution), but 29 d 12 h 44 min when seen from the Sun (synodic) and this is because in this period the Earth has revolved around the Sun (view month). 

This latest revolution period is governing Moon phases, eclipses and lunisolar tides. Since the Moon takes the same time to circle in on itself around the Earth, it always presents the same face. This is because the Earth, due to an effect called the gravitational gradient, has slowed the Moon completely.

The fact that we always see the same face of the Moon means that the Moon must rotate once in the same amount of time it takes to orbit Earth once. You can see why by walking around a model of Earth while imagining that you are the Moon.
Credit: The Cosmic Perspective.