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By Luis Gustavo. See how we research and review our content.
On 7 October 1959, the Soviet probe Luna 3 sent back the first photographs of the side of the Moon that Earth never faces. Until then, everyone who had ever looked up had seen the same hemisphere, plus a thin extra margin that the Moon’s slow wobble reveals.
The five facts below start with that hidden face and move on to a receding orbit, the Moon’s effect on the length of your day, the real nature of its dark patches, and the best way to look at craters without any special training. Each figure was checked against NASA material or published measurements.
1. You’ve never seen the “dark side” of the Moon
Tidal locking keeps one hemisphere pointed at Earth, so the far side is unseen rather than unlit, and both halves receive roughly equal sunlight over a lunar day. A slight wobble called libration lets observers on Earth glimpse about 59% of the surface over time. The rest stayed unobserved until Luna 3, and Apollo 8 astronauts became the first humans to see the far side directly, in December 1968.
When the first images arrived, scientists noticed that the far side looks different from the near side: it is rugged and heavily cratered, with few dark plains, and it is generally brighter. Proposed explanations include a thicker crust there and an uneven distribution of heat-producing elements. It also holds the South Pole–Aitken basin, one of the largest impact craters in the Solar System. China’s Chang’e 4 made the first soft landing on the far side in January 2019, and Chang’e 6 brought back the first far-side samples in June 2024.
2. The Moon is drifting away from Earth
Laser measurements bounced off reflectors left on the surface show the mean Earth–Moon distance growing by about 3.8 cm a year, based on data gathered between 1970 and 2015. The mechanism is tidal: Earth’s faster spin drags the ocean bulge slightly ahead of the Moon, and that offset bulge pulls the Moon forward into a higher orbit. Averaged over the last 620 million years, the rate was roughly 2.17 cm a year, about half today’s figure.
Total solar eclipses depend on a near-coincidence: the Sun is about 400 times wider than the Moon and about 400 times farther away. The match is already imperfect, because the Moon looks about 2.1% smaller than the Sun on average, which is why many central eclipses are ring-shaped. Estimates for when no total eclipse can occur range from about 650 million to 1.4 billion years from now, so the loss is real but very distant.
3. It’s responsible for tides (and your slightly longer days)
The same tidal friction that lifts the Moon’s orbit takes energy from Earth’s rotation. Records of ancient eclipses and astronomical observations spanning roughly 2,700 years indicate that the day lengthens by about 1.72 milliseconds per century. Laser ranging suggests the tidal effect alone is larger, near 2.4 milliseconds, but the land is still rebounding after the last ice age, and that rebound speeds rotation slightly and narrows the gap.
Most of that energy ends up as heat in shallow seas rather than in the Moon’s orbit. Of roughly 3.78 terawatts drawn from Earth’s spin, about 3.64 terawatts is dissipated in the water, and only around 0.12 terawatts goes to the Moon. A day lasting as long as a month is not on the horizon: the Sun would swell into a red giant before Earth’s day got that long.
4. Those “dark spots” have names
The dark patches are lunar maria, from the Latin for “seas”, a name from the early 1600s when observers wondered whether they held water. Galileo’s 1610 telescope observations described a rocky surface, yet the sea names stuck, and Giovanni Battista Riccioli’s 1651 map fixed the modern ones. They are basaltic plains formed when lava flooded ancient impact basins, and their iron-rich rock reflects less light than the highlands.
Maria cover about 16% of the Moon and lie mostly on the near side, which is why the face we see looks blotchy. Most of the basalt erupted between about 3 and 3.5 billion years ago, though dated samples span roughly 1.2 to 4.2 billion years. Mare Tranquillitatis, the Sea of Tranquility, is the mare where Apollo 11 landed, so one of those dark patches doubles as the site of the first crewed landing.
5. You can see craters from your own backyard
Craters stand out when sunlight hits them at a shallow angle, because shadows lengthen and expose the rim and floor. That means the best detail appears along the terminator, the line between lit and dark, and not at Full Moon, when light falls straight down and the surface looks flat. A half-lit Moon in the first or last quarter phase, viewed with even a modest telescope, shows far more relief.
The scale is bigger than most people expect. Tycho Crater is more than 85 km wide, and the whole surface is scarred by impacts from asteroids, meteoroids and comets over billions of years. Sunlit ground reaches about 127°C, while ground in darkness falls to about -173°C.
Why the Moon Takes 27 Days to Orbit but 29 to Show All Its Phases
The Moon circles Earth in about 27 days and spins once in the same time, which is the root of tidal locking. Yet the cycle of phases from one New Moon to the next lasts about 29 days, because Earth moves along its own orbit around the Sun while the Moon circles, so the Moon needs two extra days to line up with the Sun again.
The average distance is 384,400 km, and the Moon’s diameter of roughly 3,480 km is less than a third of Earth’s. These are the numbers behind everything above: its size sets its pull on the tides, and its distance sets how large it looks against the Sun.
If this topic interests you, it’s worth checking out our piece on international space station, on artemis mission, on how solar eclipses work and on meteor showers.
Want to see it for yourself?
If you enjoyed these facts, the obvious next step is pointing a telescope at the sky. For beginners, we recommend:
Gskyer Telescope, 70mm Aperture Astronomical Refracting Telescope — great value for Moon-watching and a solid entry point into amateur astronomy, tripod included.
Disclosure: this is our tracked Amazon affiliate link.
Next clear evening, skip the Full Moon and look along the line between light and dark, where long shadows turn flat grey plains into a landscape.