Why can we only see one side of the Moon?
Alan P. Boss: Is it just a coincidence that the moon's period of rotation and revolution are identical, so that we always see the same face? If not, how did this situation come to be? October 21, 1999
"The moon keeps the same face pointing towards the Earth because its rate of spin is tidally locked so that it is synchronized with its rate of revolution (the time needed to complete one orbit). In other words, the moon rotates exactly once every time it circles the Earth.
"The same forces that create tides in the Earth's oceans (from the gravitational pull of the moon and, to a lesser extent, the sun) also act on the solid body of the moon. The Earth's gravitational force on the moon distorts the moon into a slightly prolate, or football, shape; in addition the moon's intrinsic form is somewhat egg-shaped. If the tip of the football/egg does not point toward the Earth, then gravitational forces exert a torque that makes the tip point back toward the Earth (in reality, the moon oscillates a small amount around perfect alignment, a motion called the lunar libration)."
It is very unlikely that the moon started out synchronized; that would indeed be a surprising "coincidence."
https://www.scientificamerican.com/article/is-it-just-a-coincidence/
The time taken for the Moon to spin on its axis is almost exactly the same as the time it takes to orbit the Earth. Hence, the Moon always keeps the same side pointing our way. This is not a coincidence. Over billions of years, the Earth’s gravity has forced the Moon to spin synchronously with its orbit.
However, things are a bit more complicated than that. Viewed from Earth, the Moon appears to rock slowly backwards and forwards so that we see a slightly different face throughout the lunar month. There are two main reasons for this. First, the Moon’s orbit around Earth is elliptical not circular so its rotation is sometimes ahead, and sometimes behind, its orbital motion. And second, the Moon’s rotation axis is not at right angles to its orbit around the Earth so we can sometimes see ‘over’ or ‘under’ its poles. Over time this means we actually get to see about 59 per cent of the Moon’s surface.
https://www.sciencefocus.com/space/why-can-we-only-see-one-side-of-the-moon/
Alan P. Boss: Is it just a coincidence that the moon's period of rotation and revolution are identical, so that we always see the same face? If not, how did this situation come to be? October 21, 1999
"The moon keeps the same face pointing towards the Earth because its rate of spin is tidally locked so that it is synchronized with its rate of revolution (the time needed to complete one orbit). In other words, the moon rotates exactly once every time it circles the Earth.
"The same forces that create tides in the Earth's oceans (from the gravitational pull of the moon and, to a lesser extent, the sun) also act on the solid body of the moon. The Earth's gravitational force on the moon distorts the moon into a slightly prolate, or football, shape; in addition the moon's intrinsic form is somewhat egg-shaped. If the tip of the football/egg does not point toward the Earth, then gravitational forces exert a torque that makes the tip point back toward the Earth (in reality, the moon oscillates a small amount around perfect alignment, a motion called the lunar libration)."
It is very unlikely that the moon started out synchronized; that would indeed be a surprising "coincidence."
https://www.scientificamerican.com/article/is-it-just-a-coincidence/
The time taken for the Moon to spin on its axis is almost exactly the same as the time it takes to orbit the Earth. Hence, the Moon always keeps the same side pointing our way. This is not a coincidence. Over billions of years, the Earth’s gravity has forced the Moon to spin synchronously with its orbit.
However, things are a bit more complicated than that. Viewed from Earth, the Moon appears to rock slowly backwards and forwards so that we see a slightly different face throughout the lunar month. There are two main reasons for this. First, the Moon’s orbit around Earth is elliptical not circular so its rotation is sometimes ahead, and sometimes behind, its orbital motion. And second, the Moon’s rotation axis is not at right angles to its orbit around the Earth so we can sometimes see ‘over’ or ‘under’ its poles. Over time this means we actually get to see about 59 per cent of the Moon’s surface.
https://www.sciencefocus.com/space/why-can-we-only-see-one-side-of-the-moon/
