Why don’t we ever see the dark side of the moon from earth?
Because the Moon spins on its axis at precisely one revolution per revolution of Earth. This means the same face is towards Earth all the time.
In fact we can see the dark side of the Moon from Earth; it’s the black part of the crescent moon that is not illuminated by the Sun. At certain times, when the crescent is small, you can easily see the dark side glowing faintly blue, because it is being illuminated by the reflected light from the Earth.
This isn’t correct. The black part is the same face of the moon you can always see. It’s just that at times it isn’t illuminated by the Sun.
Yeah, sort of. For reasons that make no sense, popular culture seems to have decided that the “dark side of the moon” is both a Pink Floyd album and the side that faces away from the Earth. Despite that fact that the distant side of the moon is not dark, and the moon has no permanently dark side, and calling the far side the dark side actually makes no sense.
Curiously we can see some of the far side of the moon. The moon’s motion is such that it does not face exactly towards us all the time, the moon nutates, that is its axis precesses, and so over time it reveals a little bit more than one hemisphere to us. Not a lot more, but we do see, over time, more than exactly half of the moon.
And that is the dark side of the Moon. You are talking about the far side, which is a different thing.
Due to various perturbations in the lunar orbit, the dark side of the moon is only 41% of the total lunar surface.
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Nearly all of the moons in the Solar System are tidally locked, so that they always showone particular face to the planet which they orbit. About the only major moon I can think of which is not tidally locked is Hyperion, which tumbles erratically- but probably quite a few of the smaller ones rotate as well.
Not how I’ve heard people use the term, and clearly not how the OP meant it.
Right, thank you.
Oh yes, I hadn’t thought about that before. Many thanks.
Wow.
Yeah, popular culture has a lot to answer for which is why I asked the question. Thanks for the clarification.
Really? I love this MB because you get so much feedback! 
Which is funny when you consider that as Gerry O’Driscoll, the studio doorman says, “There is no dark side in the moon, really.”
Although of course he then gets it very wrong when he goes on to say “As a matter of fact it’s all dark”.
It’s very easy to see Earthshine when the moon is a thin crescent (note that having non-hazy skies helps). Through binocs or a telescope you can actually see the dim outlines of the various maria and major craters.
The first reply explains that the moon rotates once per orbit, but it doesn’t explain why. That’s covered here:
Short version: The Earth’s gravitational field distorts the shape of the moon. Back when the moon rotated more than once per orbit, this distortion caused a torque that tended to slow the rotation of the moon. This continued until the moon’s rotation slowed to the point that it always showed the same side to the earth, and the tidally-induced distortion stopped producing that decelerative torque.
Something similar is happening to the earth. The moon’s gravity distorts the earth, and because the earth is rotating faster than the moon orbits around it, that distortion produces a torque that tends to slow the rotation of the earth (it also tends to increase the orbital speed of the moon, which is gradually moving the moon to a higher orbit).
Well the moon’s albedo (optical reflectiveness) is pretty low, so even the lit-up portion of the moon is pretty dark by comparison with how bright something as reflective as the Earth or Venus would be in the moon’s position.
Yup. It’s well-illuminated, but it’s perfectly accurate to say that it’s dark in color.