# Moon Question **URL:** \ **Category:** Factual Questions\ **Created:** [August 7, 2017, 7:39am UTC](https://boards.straightdope.com/t/moon-question/792982 "2017-08-07T07:39:29Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 7:39am UTC](https://boards.straightdope.com/t/moon-question/792982/1 "2017-08-07T07:39:29Z")
Why don’t we ever see the dark side of the moon from earth? ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [August 7, 2017, 7:48am UTC](https://boards.straightdope.com/t/moon-question/792982/2 "2017-08-07T07:48:31Z")
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. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [August 7, 2017, 7:54am UTC](https://boards.straightdope.com/t/moon-question/792982/3 "2017-08-07T07:54:36Z")
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. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [August 7, 2017, 7:57am UTC](https://boards.straightdope.com/t/moon-question/792982/4 "2017-08-07T07:57:17Z")
> [@eburacum45](#): > > 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. ---
**Author:** ![Francis\_Vaughan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/francis_vaughan/32/3093_2.png) [@Francis\_Vaughan](https://boards.straightdope.com/u/Francis_Vaughan)\ **Post date:** [August 7, 2017, 8:09am UTC](https://boards.straightdope.com/t/moon-question/792982/5 "2017-08-07T08:09:48Z")
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. ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [August 7, 2017, 8:11am UTC](https://boards.straightdope.com/t/moon-question/792982/6 "2017-08-07T08:11:49Z")
> [@Princhester](#): > > 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. And that is the dark side of the Moon. You are talking about the far side, which is a different thing. ---
**Author:** ![si\_blakely](https://avatars.discourse-cdn.com/v4/letter/s/d9b06d/32.png) [@si\_blakely](https://boards.straightdope.com/u/si_blakely)\ **Post date:** [August 7, 2017, 8:11am UTC](https://boards.straightdope.com/t/moon-question/792982/7 "2017-08-07T08:11:51Z")
> [@Princhester](#): > > 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. Due to various perturbations in the lunar orbit, the dark side of the moon is only 41% of the total lunar surface. Sent from my SM-G900I using Tapatalk ---
**Author:** ![eburacum45](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/eburacum45/32/8690_2.png) [@eburacum45](https://boards.straightdope.com/u/eburacum45)\ **Post date:** [August 7, 2017, 8:16am UTC](https://boards.straightdope.com/t/moon-question/792982/8 "2017-08-07T08:16:45Z")
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. ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [August 7, 2017, 8:17am UTC](https://boards.straightdope.com/t/moon-question/792982/9 "2017-08-07T08:17:05Z")
> [@eburacum45](#): > > And that is the dark side of the Moon. You are talking about the far side, which is a different thing. Not how I’ve heard people use the term, and clearly not how the OP meant it. ---
**Author:** ![Dr.Strangelove](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/dr.strangelove/32/6613_2.png) [@Dr.Strangelove](https://boards.straightdope.com/u/Dr.Strangelove)\ **Post date:** [August 7, 2017, 8:24am UTC](https://boards.straightdope.com/t/moon-question/792982/10 "2017-08-07T08:24:32Z")
> [@si\_blakely](#): > > Due to various perturbations in the lunar orbit, the dark side of the moon is only 41% of the total lunar surface. [Lunar libration in animated form](https://upload.wikimedia.org/wikipedia/commons/c/c0/Lunar_libration_with_phase2.gif). ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:02am UTC](https://boards.straightdope.com/t/moon-question/792982/11 "2017-08-07T09:02:02Z")
> [@Princhester](#): > > 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. Right, thank you.🙂 ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:03am UTC](https://boards.straightdope.com/t/moon-question/792982/12 "2017-08-07T09:03:33Z")
> [@eburacum45](#): > > 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. Oh yes, I hadn’t thought about that before. Many thanks. ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:05am UTC](https://boards.straightdope.com/t/moon-question/792982/13 "2017-08-07T09:05:09Z")
> [@Princhester](#): > > 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. Wow. ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:07am UTC](https://boards.straightdope.com/t/moon-question/792982/14 "2017-08-07T09:07:56Z")
> [@Francis\_Vaughan](#): > > 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. Yeah, popular culture has a lot to answer for which is why I asked the question. Thanks for the clarification. 🙂 ---
**Author:** ![abashed](https://avatars.discourse-cdn.com/v4/letter/a/c6cbf5/32.png) [@abashed](https://boards.straightdope.com/u/abashed)\ **Post date:** [August 7, 2017, 9:09am UTC](https://boards.straightdope.com/t/moon-question/792982/15 "2017-08-07T09:09:51Z")
> [@si\_blakely](#): > > Due to various perturbations in the lunar orbit, the dark side of the moon is only 41% of the total lunar surface. > > Sent from my SM-G900I using Tapatalk Really? I love this MB because you get so much feedback! 😉 ---
**Author:** ![Princhester](https://avatars.discourse-cdn.com/v4/letter/p/3e96dc/32.png) [@Princhester](https://boards.straightdope.com/u/Princhester)\ **Post date:** [August 7, 2017, 9:14am UTC](https://boards.straightdope.com/t/moon-question/792982/16 "2017-08-07T09:14:35Z")
> [@Francis\_Vaughan](#): > > 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. 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”. ---
**Author:** ![John\_DiFool](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/john_difool/32/19543_2.png) [@John\_DiFool](https://boards.straightdope.com/u/John_DiFool)\ **Post date:** [August 7, 2017, 11:46am UTC](https://boards.straightdope.com/t/moon-question/792982/17 "2017-08-07T11:46:53Z")
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. ---
**Author:** ![Machine\_Elf](https://avatars.discourse-cdn.com/v4/letter/m/82dd89/32.png) [@Machine\_Elf](https://boards.straightdope.com/u/Machine_Elf)\ **Post date:** [August 7, 2017, 12:37pm UTC](https://boards.straightdope.com/t/moon-question/792982/18 "2017-08-07T12:37:25Z")
> [@abashed](#): > > Why don’t we ever see the dark side of the moon from earth? The first reply explains that the moon rotates once per orbit, but it doesn’t explain why. That’s covered here: > **[Tidal locking](https://en.wikipedia.org/wiki/Tidal_locking)** > > Tidal locking between a pair of co-orbiting astronomical bodies occurs when one of the objects reaches a state where there is no longer any net change in its rotation rate over the course of a complete orbit. In the case where a tidally locked body possesses synchronous rotation, the object takes just as long to rotate around its own axis as it does to revolve around its partner. For example, the same side of the Moon always faces Earth, although there is some variability because the Moon's orbit... 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). ---
**Author:** ![Andy\_L](https://avatars.discourse-cdn.com/v4/letter/a/c67d28/32.png) [@Andy\_L](https://boards.straightdope.com/u/Andy_L)\ **Post date:** [August 7, 2017, 12:48pm UTC](https://boards.straightdope.com/t/moon-question/792982/19 "2017-08-07T12:48:39Z")
> [@Princhester](#): > > 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”. 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. ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [August 7, 2017, 1:28pm UTC](https://boards.straightdope.com/t/moon-question/792982/20 "2017-08-07T13:28:41Z")
Yup. It’s well-illuminated, but it’s perfectly accurate to say that it’s dark in color. [Next page](https://boards.straightdope.com/t/moon-question/792982.md?page=2)