This question comes to us from Ashley in Wisconsin. Thanks for emailing us a question Ashley!
This is a great question and is really interesting to visualize. The quick answer is yes, but how it rotates is a bit different than how you might expect. Why it rotates the way it does is also very interesting.
If you do a google image search for “moon” and see the list of images that pop up, you may notice that the face of the moon looks nearly the same on every photo that you see. And this is true; we only see one side of the moon. This may lead you to think that the moon does not rotate on its axis, but you might be forgetting that the moon is also rotating around the earth as well. If you zoom out a little bit you get a clearer picture.
The moon takes about 28 days to revolve around the earth and the moon rotates on its own axis in about the same time. So, the moon is rotating on its axis, but it is rotating at approximately the same speed as it is revolving around the earth, so that the same side will always be facing us. Let’s look at a quick simulation:
In this simulation, we have the moon revolving around the earth in about 28 days (which is compressed down to 35 seconds or so) and the moon is rotating on its axis in the same time. We ignored where the sun was, so you can see rotation better and lit the scene from above. As you can see the moon is rotating, but it is rotating so that the same face is always pointed towards earth. We call this being tidally locked with the earth.
This being said, the moon does have a slight “wobble” as it rotates around the earth. This wobble looks something like this:
More info can be found here: https://svs.gsfc.nasa.gov/10836
An interesting thing about the moon is that it was not always tidally locked with earth. At one time, billions of years ago, the moon rotated on it’s axis so that both sides of the moon were visible from earth.
When you have a massive object revolving around another larger massive object, the force of gravity acts on both of them. In the case of the Earth and Moon, the moon pulls on earth which causes the tides in the ocean. The Earth also pulls on the moon, and although the moon doesn’t have water to have tides, the earth deforms the moon slightly making the the side facing Earth slightly longer. This deformation of the moon causes a slight “friction” to the rotation, and after a while, and by a while I mean a few million years, the rotation slows to match the revolution around the Earth.
Also this tidal locking isn’t unique to our moon. Many other moons within the solar system are tidally locked by the same mechanism as our moon. Here is a quick list of other moons that are tidally locked in our Solar System:
- Phobos and Deimos around Mars
- Metis, Adrastea, Amalthea, Thebe, Io, Europa,Ganymede, and Callisto around Jupiter
- Pan, Atlas, Prometheus, Pandora, Epimetheus, Janus, Mimas, Enceladus, Telesto, Tethys, Calypso, Dione, Rhea, Titan, and Iapetus around Saturn
- Miranda, Ariel, Umbriel, Titania and Oberon around Uranus
- Proteus and Triton around Neptune
- And Pluto and Charon are both locked together
Even one of the Earth-like planets found in the Goldilocks Zone orbiting our closest star, Proxima Centauri, is thought to be tidally locked, meaning one side of that planet would have perpetual day, and one side would have perpetual night.
This tidal locking is found all across the universe, from moons, to planets to stars.
Thanks for reading!
Further info and links:
Earth-like planet found orbiting the star next door
Tidal Locking via Wikipedia
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