Once I heard that from earth we can observe about 60% of moon’s surface. Though the face that is turned to use os always the same. Is it true? And if so why?
In: Earth Science
The moon in tidally locked, meaning it’s own rotation matches that of earths. So as it rotates around the earth the same face always points in towards the earth. But it’s not perfect, so it appears to wobble a bit, rotating a few degrees left and right at different points in it’s orbit. This means that at times you will see a tiny bit more of one side and a tiny bit less of the other. This effect is not immediately evident to a casual observer but with even a low powered telescope if you pay very close attention to landmarks on the moon’s surface, especially towards the edges, you can observe this for yourself.
The moon is tidally locked to the Earth, so that as it rotates around us, the same side of the moon always faces the Earth. The why is kind of complicated, but lets just say that the moon’s core is lopsided, and the heavier part of the core always faces Earth due to gravity.
From our vantage point here on Earth, we can see about 60% of the surface as the moon orbits us. The far side of the moon (wrongly called the dark side of the moon), always faces away from us, so in order to see that 40%, we had to send a camera back there on a rocket.
Its due to something called Libration, basically wiggling of the moon which lets us see around the normal edges
The moons rotational axis is tilted by about 7 degrees so this lets us see a bit more of it as it travels up and down during its orbit. The moon’s orbit is not a perfect circle so its rotation sometimes lags or leads its orbital position when its close/far away.
The result is [a wobbly moon that you can see over half of while mainly looking at just one side](https://upload.wikimedia.org/wikipedia/commons/b/ba/Lunar_libration_with_phase_Oct_2007_450px.gif)
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