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This effect is called Lunar Libration. The word
libration comes from the word for "balance" or "scales" as what we see is
a rocking motion.
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Libration
Imagine you were on the surface of the Sun. What would the Earth look like?
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Throughout the year the Earth would appear to tilt up and down as shown here. (It would also be spinning round but I'm ignoring that here.) This is of course because of the tilt of the Earth. Notice that if you live in the UK the Sun is almost overhead in June. Notice also that from the Sun you would be able to see the North and South poles at different times of the year. |
So how come we can see more than 50% of the Moon, even though the same face of the Moon is facing us all the time?
The answer is that the Moon's spinning axis is also tilted. Not as much as the Earth's, only 1.5 degrees, but because of this we actually see about 59% of its surface from Earth throughout its orbit.
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This effect is called Lunar Libration. The word
libration comes from the word for "balance" or "scales" as what we see is
a rocking motion.
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From different parts of the Earth we can see different parts of the Moon.
