The far side of the Moon
The dark side of the moon, also called the far side, is the hemisphere of the moon that faces away from Earth. Due to tidal locking—where the moon's rotation period matches its orbit around Earth—we always see the same side of the moon from Earth. The term "dark" means "unseen" rather than unilluminated; both sides receive sunlight. The far side remained unknown to humans until 1959, when Soviet spacecraft Luna 3 photographed it for the first time. Today, it matters because exploring the far side reveals different geology than the near side, including more craters and fewer flat plains called maria. The far side has also become scientifically important for placing instruments like radio telescopes, where Earth's radio interference cannot reach them.
Sources
- en.wikipedia.org: “The far side of the Moon, also called the dark side of the Moon, is the hemisphere of the Moon that faces away from Earth; the opposite hemisphere being the near side.”
- en.wikipedia.org: “Due to tidal locking, the time it takes for the Moon to orbit the Earth once is equal to the time it takes for the Moon to rotate once, thus, the far side of the Moon never fully comes into view from Earth's surface.”
- en.wikipedia.org: “The far side has sometimes been called the "dark side of the Moon", where "dark" means "unseen" instead of "unilluminated".”
- en.wikipedia.org: “The remaining 82% remained unobserved until 1959, when it was photographed by the Soviet Luna 3 space probe.”
- en.wikipedia.org: “Compared to the near side, the far side's terrain is rugged, with a multitude of impact craters and relatively few flat and dark lunar maria ("seas"), giving it an appearance closer to other barren places in the Solar System such as Mercury and Callisto.”
- en.wikipedia.org: “Astronomers have suggested installing a large radio telescope on the far side, where the Moon would shield it from possible radio interference from Earth.”