What is the period of rotation of the Moon?

Question posed by "hh" on the Ask a question! page

A body's period of rotation is how long it takes to turn once around its own axis of rotation relative to the background of stars.

The Moon's rotational period is a bit more than 27 1/4 days*, just under four weeks, or a month ('moonth').

Coincidentally** the Moon's orbital period around the Earth is about the same, which means that on Earth we only ever see the same face pointing towards us.

With that in mind, what percentage of the Moon's surface do you think we see from Earth***?

* That's Earth days, naturally.
** Well, not really: there's a scientific reason for it.
*** The answer's probably not what you think it is.


  1. Is it something like 70%? I thought it was more than 50% anyway.

    Also, I think we should actually call them moonths.

  2. From memory I don't think it's as large as 70%, but it's certainly larger than the 50% or so you'd expect. Can you remember what Mr Fry said was the reason in that particular edition of QI? ;-)

    'Moonth' has a certain charm to it, doesn't it?


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