Every person who has ever lived has seen the same face of the moon. The same craters, the same dark plains, the same bright highlands. For all of recorded history, nobody knew what was on the other side. It could have been anything. When spacecraft finally flew behind the moon in 1959, what they found was genuinely surprising: the far side looks almost nothing like the side we know.
Why We Only See One Side
The moon rotates on its axis at exactly the same rate it orbits Earth, completing one rotation every 27.3 days. This means the same hemisphere always faces us. The phenomenon is called tidal locking, and it is not a coincidence. It is the inevitable result of gravitational interaction between two bodies over a long enough period.
Early in its history, the moon rotated faster. Earth's gravitational pull created tidal bulges in the moon's rocky body (not water tides - rock tides). These bulges acted as a brake, gradually slowing the moon's rotation until it matched its orbital period. Once synchronised, the braking stopped. The process took perhaps a hundred million years, and it was complete billions of years ago.
Tidal locking is common in the solar system. Most large moons of Jupiter and Saturn are tidally locked to their planets. Pluto and its moon Charon are mutually locked, each showing the same face to the other. Earth itself is slowly being locked to the moon, though the process will take so long that the sun will likely expand and consume both bodies before it completes.
What "Far Side" Actually Means
The far side is not the "dark side." Every part of the moon receives sunlight. During a new moon, when the near side is completely dark from our perspective, the far side is in full sunlight. The far side experiences the same cycle of day and night as the near side, just offset by about two weeks.
The phrase "dark side of the moon" became popular through culture, most notably Pink Floyd, but it has always been misleading. The far side is dark only in the sense of being unseen, not unlit. Scientists and space agencies consistently use "far side" to avoid this confusion.
There is a subtle wrinkle: the moon wobbles slightly as it orbits, a set of oscillations called libration. These wobbles let us peek just past the edge, so over time we can actually see about 59% of the moon's surface from Earth, not exactly 50%. But the remaining 41% was completely unknown until the space age.
The First Photographs
On October 7, 1959, the Soviet spacecraft Luna 3 swung around the moon and photographed the far side for the first time. The images were grainy and low-resolution by modern standards, but they revealed something immediately obvious: the far side had almost no maria - none of the large, dark, flat basaltic plains that dominate the near side and give the "Man in the Moon" its familiar features.
Instead, the far side was almost entirely covered in heavily cratered highland terrain. It was brighter, rougher and more uniform than the near side. The contrast was so stark that scientists initially suspected a camera error. Subsequent missions confirmed what Luna 3 had shown: the two hemispheres of the moon are fundamentally different.
Why the Two Sides Look So Different
The maria on the near side formed when ancient asteroid impacts cracked the crust deeply enough for magma to well up from the interior and flood the impact basins. These volcanic eruptions created the dark, smooth plains visible from Earth. The question is why this happened on the near side but not the far side.
The leading explanation involves the moon's crust. The far side's crust is significantly thicker than the near side's, in some places nearly twice as thick. When large impacts struck the far side, the crust was too thick for magma to break through. On the near side, the thinner crust cracked more easily, allowing volcanic flooding.
Why the crust is thicker on the far side is itself a question with several competing theories. One suggests that early in the moon's history, when both the Earth and moon were still partially molten, heat radiating from the hot Earth kept the near side crust thinner by slowing its cooling. The far side, facing away from Earth's heat, cooled and thickened faster. Another theory proposes that a second, smaller moon collided with the far side early on, plastering extra crustal material across that hemisphere.
The South Pole-Aitken Basin
The far side hosts one of the largest and oldest impact structures in the entire solar system: the South Pole-Aitken Basin. It stretches roughly 2,500 kilometres across and reaches depths of over 8 kilometres. For comparison, it could contain most of Western Europe.
Despite its enormous size, the basin's floor was never flooded by lava in the way near-side basins were. The far side crust, even after being excavated by one of the most violent impacts in lunar history, remained too thick for magma to reach the surface. The basin instead offers a rare window into the moon's deep interior, with some of its floor material thought to have been excavated from the upper mantle. Future sample return missions targeting this basin could reveal information about the moon's internal composition that is impossible to obtain anywhere else.
China's Chang'e 4: Landing on the Far Side
On January 3, 2019, China's Chang'e 4 mission became the first spacecraft to land on the far side of the moon. The landing site was Von Karman crater, inside the South Pole-Aitken Basin. Because the far side never faces Earth, direct radio communication is impossible. China solved this by positioning a relay satellite, Queqiao, at the second Earth-Moon Lagrange point, where it maintains a line of sight to both the far side and Earth.
The Yutu-2 rover deployed by Chang'e 4 has been operating on the far side since landing, studying the composition of the surface material and the radiation environment. Among its findings: the subsurface soil in Von Karman crater differs from anything sampled on the near side, supporting the theory that the South Pole-Aitken impact excavated material from deep within the moon.
Chang'e 6, launched in 2024, went further: it collected and returned samples from the far side to Earth, a first in space exploration. Analysis of these samples is ongoing and may reshape understanding of the moon's formation and the early solar system.
The Far Side as a Future Observatory
The far side has one property that makes it uniquely valuable for science: it is the only place in the inner solar system that is permanently shielded from Earth's radio noise. Every radio station, mobile phone, radar system and WiFi router on Earth contributes to a constant electromagnetic fog that interferes with sensitive astronomical observations. On the far side, with 3,400 kilometres of solid rock blocking all of it, the radio environment is the quietest available anywhere near Earth.
Proposals for far-side radio telescopes have existed since the 1960s. A low-frequency radio array on the far side could detect signals from the cosmic dark ages, the period between the Big Bang and the formation of the first stars, which cannot be observed from Earth or even from Earth orbit because our planet's ionosphere and radio pollution block the relevant frequencies.
NASA's Artemis programme and China's lunar exploration programme both include long-term plans for far-side infrastructure. Whether a radio telescope is built there within this decade or the next, the far side's unique silence makes it a question of when, not whether.
For most of human history, the far side was the largest unseen place we knew existed. Half a world that we could calculate must be there but could not examine. When we finally looked, we found that the moon had been showing us its more interesting face all along. The far side is plainer, rougher, more uniform. But it holds secrets the near side cannot offer: the deepest impact basin in the solar system, a geological record uncontaminated by volcanic flooding and the quietest listening post available to a civilisation that has filled its own sky with noise.