09/09/2026
Last week, we wrote about Venus and the reason it rotates so slowly, including how the planet is partially tidally locked. The Moon, as you may know, is completely tidally locked, meaning that we only ever see one side of the Moon from here on Earth. This week, we’re going to dive a little deeper into why we only see one side of the Moon, what the other side of the Moon looks like and why, and how common it is for a celestial object to be tidally locked with another object!
⭐ Why do we see only one side of the Moon from Earth?
We see only the “near side” of the Moon because it rotates on its axis in the exact same amount of time it takes to orbit Earth, due to something called tidal locking. Tidal locking (sometimes called synchronous tidal locking) is a gravitational phenomenon that can be difficult to picture, but it’s sort of like when you spin in circles with your friend while you’re holding hands and facing each other. You’re both spinning and completing individual rotations, but you stay facing each other because your orbital period (the time it takes to complete one full circle around you and your friend’s pivot point) exactly matches your rotation period (the time it takes your body to rotate 360°).
A larger, more massive object will pull harder on the near side of a less-massive orbiting object, which stretches it into an almost egg-like, oblong shape called a tidal bulge. The smaller object will likely start out spinning faster than it orbits, so the gravitational bulge will be slightly out of alignment with the gravitational pull of the larger object. The gravitational pull on the mis-aligned tidal bulge acts as a brake that slowly slows down the orbiting object’s spin until its rotational period matches the orbital period, at which point the rotation stays locked. So, just like spinning with your friend, we always see the same face of the Moon, even though it is rotating.
⭐ If you were on the Moon, would you always see the same side of Earth?
No, you would see all sides of Earth as it rotates because it is spinning relatively faster on its own axis. What’s really cool though is that, from the surface of the Moon, Earth would never rise or set – it would remain in the same position in the sky at all times because your viewpoint from the Moon is rotating at the same exact speed that the Moon is orbiting Earth. You would also see Earth go through phases like we see with the Moon, such as a “crescent Earth”, “new Earth”, or “full Earth”!
⭐ Is there such thing as the “dark side” of the Moon?
Sorry, Pink Floyd, but there is no “dark side” of the Moon. There is a far side though, and people historically thought it was dark because the far side is hidden from our view and facing the dark blackness of space. In reality, both sides of the Moon receive exactly the same amount of sunlight and, when the Moon is in a new moon phase, the far side is fully illuminated by the Sun.
⭐ Why does the far side of the Moon look different from the near side?
If you’ve ever seen images or maps that show both sides of the Moon side-by-side, you may have noticed that the near side has larger patches of relatively smooth surface and fewer craters. This is primarily because of crustal asymmetry that developed as the Moon was forming and cooling. The Moon formed from the debris left over from the collision of a large object and Earth about 4.3 billion years ago, when the solar system was still pretty young. Without going into too much detail, that process left the near side of the Moon with a thinner, hotter crust while the far side had a thicker, cooler crust. The near side had more volcanic eruptions that erased many of the craters that impacted the Moon, resulting in a smoother surface with large mare; the large patches of dark-colored volcanic rock. The far side’s thicker and cooler crust preserved the impact craters without overprinting them with large volcanic eruptions.
⭐ Are any other objects in our solar system tidally locked?
Tidal locking is actually very common! In fact, every moon in our solar system that is massive and close enough to its parent planet is tidally locked. Notable pairings include:
▪️Mars and its moons, Phobos and Deimos
▪️Jupiter and its four Galilean moons – Io, Europa, Ganymede, Callisto
▪️Saturn and its moon Titan, Enceladus, Mimas, etc.
▪️Uranus and its major moons – Ariel, Umbriel, Titania, Oberon
▪️Neptune and its moon, Triton
And though it is no longer considered a planet, Pluto is actually mutually tidally locked to its moon, Charon. Pluto and Charon are relatively close in mass, so both objects act as gravitational brakes on each other.
While we’re on the topic of the “dark side of the Moon” though, we want to remind you to check out our Pink Floyd show at the Dome! It features awesome visuals set to the entire Dark Side of the Moon album and is one of our favorite shows we’ve ever had! Scroll down to the Pink Floyd section for more information and a link to purchase tickets!
📷: The near side of the Moon (left) and far side of the Moon (right). Via NASA LRO/Jatan Mehta.
📽️: An animation showing the difference in view before and after Earth-Moon tidal locking. Via Vi Nguyen, NASA Goddard Space Flight Center.
