The reverse side of the Moon
As is generally known, the Moon is not a disc but a sphere and one could ask the question if we actually get to see different sides of this Moon sphere? The answer is: no! At least this is true for the observer from Earth.
Indeed, we always see one half of the Moon. This is because the Moon is locked into the Earth rotation. This is called »synchronous rotation«. It means that we are never able to see the side of the Moon facing away from us. And until it was possible to photograph the reverse of the Moon with space probes, nobody knew what we would find or how it would look.
The first images were provided by the Russian space probe Luna 3 at the end of 1959. These photos are of historic significance, even though of poor quality, due to the radio technology used (see right picture).
Only in the course of the Apollo 8 mission in 1968, the astronauts William Anders, James Lovell and Frank Borman were the first humans to see the reverse of the Earth’s moon with their own eyes. Altogether, they circled the Moon ten times during this mission and read the first part of the Genesis from the Bible for the people on Earth, on Christmas Eve of 1968. »In the beginning God created the heavens and the earth …«
Since we began documenting the reverse/far side of the Moon, we know that it looks quite differently in comparison to the front/near side. The far side has only a fraction of dark spots, the so called lunar mares, that we are able to see at all times when looking at the front of the Moon. These spots consist of solidified lava and were possibly caused by impacts of asteroids (virtually large meteorites), that hit the Moon’s surface approx. four billion years ago.
Different when comparing the front and reverse side are also the altitude levels of mountains and valleys, distribution of gravitational fields and many more. The always improving images of today’s space probes continuously support new insights (see picture; left: front/near side, right: reverse/far side).
Sometimes we also speak of the »dark side of the moon« (not only Pink Floyd!), which would be the incorrect term for the reverse of the Moon, as this side is also exposed to sunlight, just like the front. This term would be correct if it relates to the »unexplored« aspects, meaning the secrets and open questions that still remain.
Every now and then it is suitable when we people admit that we are far from knowing everything …