The patterns of the dark craters on the near side of the Moon have spurred the imagination of observers from all cultures: Some visualize a woman, others a rabbit, or, like most of us, they see the “Man in the Moon.”
The explanation as to why we always see the Man in the Moon – that is, why we only see one side – is that tidal forces caused the Moon to slow its spin until it reached the present point. It now takes the same amount of time to rotate around its own axis as it does to revolve around Earth. It is this synchronous rotation that causes the moon to “lock” with Earth, with one hemisphere constantly facing us.
But Prof. Oded Aharonson of the Weizmann Institute’s Center for Planetary Science, together with Prof. Peter Goldreich of the California Institute of Technology and Prof. Re’em Sari of the Hebrew University of Jerusalem wanted to know whether there is a reason why this particular half of the Moon locked with Earth or if it is pure luck that it didn’t turn its “back” on us?
Unlike the near side, which is covered in dense craters, the far side is made up of more mountainous regions, and these differences affect the Moon’s gravitational energy. Taking this into consideration, the scientists, through careful analysis and simulations, have shown that it is not coincidence but rather, the Moon’s geophysical properties that determine its orientation. Their findings have recently been published in Icarus. A more detailed description can also be found on our website: http://wis-wander.weizmann.ac.il/why-do-we-see-the-man-in-the-moon-oded-aharonson