Since 1973, Roger Waters has been informing us that he’d see us on the dark side of the Moon—but if you’ve ever found yourself wondering whether there really is a dark side of the Moon, scientists have some bad news for you: Not quite. (Apologies to Pink Floyd.)
Interestingly, though, the issue isn’t as simple as the so-called dark side of the Moon not existing at all. There isn’t a side of the Moon that’s permanently in shadow; however, that doesn’t mean that the Moon itself is lit at all times, either. When most people reference the “dark side of the Moon,” what they really mean is the far side of the Moon—which definitely isn’t the same thing.
Here’s what the deal with the so-called “dark” side of the Moon.
The Far Side, Not the Dark Side
Fun fact: Whenever we see the Moon from Earth, we’re always looking at the same side—no matter where on the planet you are or what time it happens to be. Only one side of the Moon ever presents its face to the Earth, because it’s what’s referred to as tidally locked to the planet. Tidal locking occurs when the speed of a celestial body’s rotation around its axis matches the rate at which it orbits its partner. In this case, we’re talking about the Moon rotating around its axis at the same speed that it orbits the Earth. The Moon takes about 27 days to complete both actions.
As a result of tidal locking, the Moon is said to have a near side and a far side. The near side is the side we perpetually see from Earth, while the far side is the side that perpetually faces away from Earth. But neither side of the Moon is permanently dark; the Moon experiences night and day, just as the Earth does.
Night and Day
It’s true that the periods of light and shadow that make up lunar days and nights last quite a bit longer on the Moon than they do on Earth; according to EarthSky, each is about 14 days in length according to how we measure time on Earth. But either way, the point is that both sides see an equal amount of sunlight and shadow, depending on where the Moon is in its orbit.
From where we stand on the surface of the Earth, the phases of the Moon provide the clearest indication of this phenomenon in action. When we see a full moon, the Earth is positioned between the Sun and the Moon, meaning that the Moon’s near side is in full sun and the far side in shadow. As How Stuff Works analogously puts it, “Imagine that you have your back to a light source and someone is standing in front of you. You’d be able to see that person clearly. That’s the same as a full moon.”
When there’s a new moon, however—that is, when the Moon appears totally dark when viewed from the Earth’s surface—the Moon is positioned between the Earth and the Sun, meaning that its far side receives full sunlight while the near side is in shadow. In How Stuff Works’ analogy, this situation is similar to what happens when someone stands between you and a light source: “You wouldn’t be able to make out any details,” the site explains, “but you could see the person in silhouette. That’s exactly what a new moon is.”
The Mysteries of the Moon
Much about the far side of the Moon remains a mystery to us, due to the fact that it’s a lot harder to get to than the near side. (Not that either side is particularly easy to get, but you get the idea.) In fact, for this reason, you might sometimes see the explanation that the word “dark” in the phrase “the dark side of the Moon” refers not to whether the far side is lit or not, but rather means something more like “unknown.” However, a handful of missions executed by the space programs of a few different countries have managed to take photographs of the far side of the Moon over the years—and what we’ve seen so far has been relatively surprising.
The first photographs ever taken of the Moon’s far side were captured in October of 1959 by the Luna 3 spacecraft launched by the former Soviet Union. Although the images were quite rough by today’s standards, one thing was easy to see right off the bat: Unlike the near side of the Moon, the far side had almost no lunar maria—the basaltic plains composed of rapidly-cooled lava that appear to observers as dark patches on the Moon’s surface. (These maria make up the Man in the Moon.) What the far side did have, though, was a huge number of craters—many more than the near side had, some of which were as large as small countries, according to Space.com.
In 1965, the Soviet Union launched another mission, Zond 3, which provided much higher quality images of the far side of the Moon than the Luna 3 mission had; these images made mapping the entire lunar surface possible. Then, in 1968, NASA’s Apollo 8 mission out of the United States allowed humans to set eyes on the Moon’s far side for the very first time. Astronaut William Anders described it as follows: “”The backside looks like a sand pile my kids have played in for some time. It’s all beat up, no definition, just a lot of bumps and holes.”
On Jan. 3, 2019, China’s space program achieved a new first: When the Chang’ e 4 robotic lander touched down, it became the first soft landing successfully made on the far side of the Moon. It’s still up there as of May 2020; its Yutu 2 rover has so far explored around 425 meters (about 1,395 feet) of the celestial body’s surface, waking and working during the lunar days and hibernating during the lunar nights. A trove of images captured during the mission was released in January of 2020, just after the first anniversary of the Chang’ e 4’s landing, though, showing that the rover has been hard at work.
Will we ever put an actual human on the far side of the Moon? That remains to be seen—but if it ever happens, at least those lucky astronauts have the perfect song to play while they make the landing already picked out.