For many of us, the Dark Side of the Moon means Pink Floyd. But in 1959, it meant the third lunar spacecraft launched from the Soviet Union had captured the first images of the far side of the moon.
We call it the dark side of the moon because Earth’s gravity has locked the moon and Earth together. As a result, mankind had only ever seen about half of the surface of the moon.
Luna 3 was a radio-controlled spacecraft. However, on 06 October 1959 it “dipped under the pole, blocking all of its communications with Earth and leaving the probe to its automatic systems.” On Earth, we could see only a sliver of the moon, meaning that the far side was facing the sun.
Luna 3 knew it was behind the moon because a photocell detected the sun’s light. For about 40 minutes on October 7th, Luna 3 photographed about 70 percent of the dark side of the moon from about 40,000 miles above the lunar surface.
6) And it gets WILDER because these photos were then moved to a little CHEMICAL PLANT to DEVELOP AND DRY THEM. That's right, Luna 3 had a little 1 Hour Photo inside. Now you're thinking, well, how do you get those actual photos back to the Earth?
— Kevin Hainline (@Kevin_Hainline) October 2, 2019
On 18 October 1959, Luna 3 successfully faxed 17 photos, made with a 35mm camera, to Earth through space. It “transmitted the lightness and darkness information line-by-line via frequency-modulated analog signal—in essence, a fax sent over radio.”
The “temperature-resistant and radiation-hardened photographic film” the camera used had been an unintended gift from America. In 1956, the U.S. had launched a short-lived Air Force spy balloon program. Soviet scientists reverse-engineered the film found in captured balloons.
Those photos, although of low resolution, divulged a surface very different from the side of the moon facing Earth. There were only two dark regions, now named Mare Moscovrae (Sea of Moscow) and Mare Desiderii (Sea of Dreams).
The photos from Lunik 3 also hinted at an enormous crater near the south pole on the far side of the moon, one which later surveys confirmed. This crater is now known as the South Pole–Aitken basin, one of the largest impact craters in the solar system. It is 2,600 kilometers (1,616 miles) wide, covering an area equivalent to over half the size of the United States. It is twice as deep as Mount Everest is tall, and it is the only place on the moon where the lower crust lies exposed.
Moscow lost contact with Luna 3 on 22 October 1959 and shared its photos with the world on the 26th.
Fifty years later, NASA launched the Lunar Reconnaissance Orbiter.