Spark image

Orbit of the Moon

QUESTION:
I know that the Moon orbits the Earth, but does the Moon rotate on its axis, like the Earth does every 24 hours?


Answer

The answer is that the Moon does rotate on its axis but not once in 24 hours.

This is quite easy to observe.

If you look at the Moon from night to night you will see that the phase changes, form new Moon to full Moon and back again. However if you look at the features that can be seen in the parts of the Moon illuminated by the Sun these do not change.

This is because the Moon the same length of time to orbit the Earth as it does to rotate once on its axis (28.3 days).

You can demonstrate this for yourself by putting a stool in the middle of a room to represent the Earth. Then you stand facing the stool (you are the Moon).

Now move once round the stool slowly making sure that you always face the stool. You will have 'orbited' the stool once and an observer on the stool will always see you face at any point in the orbit.

Now do the same again but this time notice what you are doing compared with the room. As you move round the stool always facing inwards towards it you will find that you are facing different walls of the room. In fact while you orbit the stool once you will have turned round once as well. Your period of rotation is the same as your orbit period round the stool.



schoolphysics: Moon facing the Earth animation

To see an animation of the why you always see the same side of the Moon from the Earth click on the animation link.


 
 
 
© Keith Gibbs 2007