Secrets from the other side of the moon

The moon shows us each month her smiling face "Man in the moon", illuminated by the sun in varying degrees during its orbit around us. However, thanks to its orbital dynamics, we can never see this hemisphere of the Earth. The other hemisphere – the "far side" – is constantly hidden from us.

Well, this is not strictly true. Libration, which is the gentle "wobbling" of the moon in the sky caused by changes in its position on its elliptical (ie non-circular) orbit around the Earth, means that we can see small bursts on the other side – we can actually observe 59% of the moon's surface from Earth at different times of the year. But until the first space missions on the moon flew around our natural satellite, what was on the other side was a mystery.

It is often wrongly thought that the hidden face of the moon is plunged into darkness. Rather, he experiences the day / night cycles, as does the near side. When we see half of the moon illuminated by the sun, which gives it a half-crescent or crescent shape in the sky, half of the moon on the other side is illuminated at the same time. When the moon is new, the far side is in the light of day. When the moon is full, it is dark on the other side. [China’s Chang’e 4 Moon Far Side Mission in Pictures]

The reason we only see one face is because of a phenomenon called "tidal locking". The moon rotates about its axis approximately once every 27 days, which corresponds to the time required to orbit the Earth. That means it's spinning at a rate that means we always see the same face, more or less, when it moves around the Earth.

"There are two weeks of daylight and two weeks of night on every point of the lunar surface," said Charlie Duke, pilot of the lunar module of the Apollo 16 mission, at All About Space. "It was the early morning of the moon 's day at the landing site of Apollo 16, which was called Descartes. We were the fifth mission to land on the moon, and I can say that it's really a dramatic place. "

Our first glimpse of this mysterious distant side began early in the space race, thanks to the Luna 3 spacecraft of the Soviet Union, nearly 60 years ago. In 1959, just two years after placing Sputnik 1 in orbit, Russian engineers managed to send the satellite, which was impolite, to current standards, orbiting the moon and, for the first time, we watched well the mysterious far side. .

Luna 3 took 29 full-face movie footage, which was photographically developed, fixed and dried on board – remember, it was well before multi-megapixel cameras. Ironically, the film used was stolen from American espionage balloons because it had to be solid and radiation-hardened.

The spacecraft, using a combination of two camera systems, a wide field and a narrow but higher resolution field, and a coarse on-board scanner, could then transmit the processed images, which were scanned locally from the photographs, to the receiver. station in the former Soviet Union. Although only 17 of the 29 catches were successfully broadcast on Earth, six of which were considered good enough to be released, they proved to be a revelation.

Moon Master: An easy quiz for the crazy

For most of human history, the moon was largely a mystery. It has aroused fear and fear and to this day is the source of myth and legend. But today, we know a lot about our preferred natural satellite. Do you?

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These six images covered 70% of the hidden face and opened up a new perspective on the lunar surface. It was almost immediately obvious that the dark areas that form the face of Man in the Moon are almost completely absent from the far side. These dark areas are basaltic plains called "pools" created by volcanic activity on the moon billions of years ago. Instead, the far side was littered with craters, even more so than the near side, and some of these craters were about the size of a small country. The Soviets began to name many of the features they saw for the first time, an act that provoked controversy at the time of what is known as the climax of the Cold War.

We already had an idea of ​​one of these vast new craters, which is actually one of the few mares on the other side. The most subtle allusion to Mare Orientale, one of the largest known impact craters, appearing on the branch of the moon, is known since its "discovery" by Julius Franz in 1906 and can be observed during good librations when this part of the moon is swinging towards us. [The Moon: 10 Surprising Lunar Facts]

The sight of Luna 3 shows how large the Eastern impact crater was and looked like a bubble. It was nearly 900 km wide, which is roughly the length of the United Kingdom, and was caused by an asteroid impact, whose width was estimated at about 64 km there is a little less 4 billion years old. the resulting giant crater, called the "impact basin", was then filled with volcanic lava.

In 1965, another Soviet mission, Zond 3, flew over the moon with a much better camera than Luna 3 and the ability to conduct more detailed scientific observations, including spectroscopy. Zond 3 produced 23 very detailed photographs of the hidden side of the moon, which allowed us to build one of the first detailed maps of the lunar surface.

Meanwhile, NASA was progressing at a phenomenal pace in its Apollo program. After President Kennedy's statement that the United States would put a man on the moon and bring him safely back to Earth by the end of the 1960s, in December 1968, NASA was ready to send three people – Frank Borman, Jim Lovell and Bill Anders – all around the moon and back for the Apollo 8 mission. They became the first humans in history not only to escape from a low Earth orbit. but also to see the elusive distant.

This is how Lovell described the lunar surface: "The moon is essentially gray, no color, it looks like plaster of Paris or a kind of greyish beach sand, we can see enough details. as much contrast between this and the surrounding craters.All craters are rounded.There are several, some are newer, many look like – especially the round ones – [they were] struck by meteorites or projectiles of some sort. " [Apollo 8: NASA’s First Crewed Trip Around the Moon in Pictures]

When the Apollo 8 space shuttle flew over the moon, the signal to Earth was cut off for about 10 minutes. This loss of signal was a difficult time for the flight crew and the mission control; Apollo 8 was alone and truly cut off from the Earth, venturing where no human had ever gone before. As the astronauts returned to the other side, many members of the Mission Control Flight Team in Houston breathed a sigh of relief.

Charlie Duke describes what it was like to fly beyond the moon.

"The computer told us that we were not in contact with the Earth and that we had a loss of signal," he says. "Then, suddenly, the sunrise was the most spectacular ever seen.In Earth's orbit, the sun shines on the horizon or the atmosphere of the planet, and it gets brighter and brighter. The moon is different, however, there is an instantaneous solar light with long shadows on the lunar surface.The hidden face of the moon was very deep there.I would not have wanted to land at the moon. back of the moon. "

After the success of Apollo 8, Apollo 9 returned to vital tests of the lunar module in low Earth orbit, so that the next astronauts to visit the outside were Gene Cernan, John Young and Tom Stafford aboard Apollo 10 in May 1969. month before the historic landing of Apollo 11.

However, as they flew over the moon, the trio of astronauts encountered a strange phenomenon, which NASA has been forced to re-explain in recent years through documentaries on conspiracy theory broadcast on American television . The facts were known since the 1970s.

These "strange events" on Apollo 10 were obvious in the form of very strange sounds. The radio systems aboard the Apollo Space Shuttle were rudimentary compared to modern standards, although they were at the forefront of technology at the time. According to most astronauts, the lunar and control modules were relatively noisy environments, with bumps and detonation combined with buzzing fans and engine noise. What the crew of Apollo 10 heard through the radio systems baffled them. They described it as being almost similar to that of an electronic instrument called Theremin, often used in scary science fiction B-movies of the 50s and 60s, as well as on the song "Good Vibrations" "from Beach Boys. Research has since shown that the sound was nothing more than a scrambling effect caused by the embedded radio communication systems of the 1960s. [Lunar Legacy: 45 Apollo Moon Mission Photos]

With the moon landings, two astronauts went to the surface, a third remained on board the control module to orbit the moon, although they all had the chance to turn around. the moon and see the farthest side before landing. Orbital solo trips by Michael Collins (Apollo 11), Dick Gordon (Apollo 12), Stuart Roosa (Apollo 14), Al Worden (Apollo 15), Ken Mattingly (Apollo 16) and Ron Evans (Apollo 17), who were The unsung heroes of the Apollo missions are among the most courageous feats ever performed by astronauts. They spent days making fairly detailed lunar observations in orbit, mapping features that no one had seen before.

Al Worden is often quoted as saying that his time alone was among the best he had had during the Apollo 15 mission.

"It was good to get rid of these guys, as you can imagine. Being stuck in a car the size of a family car for more than a week, there were a lot of people up there. Once Dave [Scott] and Jim [Irwin] On the left, I felt as if I had a real space to begin my important work of mapping the lunar surface. But the distant side, the views at times, when the sun and the Earth are blocked, look like nothing you can imagine. The number of stars you see is amazing. it's like a blanket of white and you know that each of them is a full sun. "

An often asked question to Apollo astronauts and flight crews is: Why were all the missions closely located? [Moon Master: An Easy Quiz for Lunatics]

"We wanted to be in contact with the Earth, so we could not land on the other side of the moon," says Charlie Duke. If something had gone wrong while the astronauts were on the surface, they would not have been able to communicate directly with Earth. It would not be a problem today, because satellites could be put into lunar orbit to relay communications.

The remote side is of growing interest to scientists and future human missions. Indeed, the possibilities for the hidden face of the moon are vast. For many decades, the scientific and astronomical community wanted to place radio telescopes and optical telescopes on the other side. The observatories located on the other side would be protected not only from radio disturbances caused by humans, but also from daylight on our planet. The telescopes could be built inside craters to avoid solar radiation and would provide us with an unprecedented insight into the depths of the depths of the universe.

Moreover, we do not really understand the processes that make the far side look so different. Why is it so marked by the impact craters and the lack of volcanic mares is even more amazing when you know that when the moon formed, it was much closer to the Earth and was not necessarily locked at the time, which meant nothing special about the hemisphere, we call the far side.

Today, NASA's lunar reconnaissance orbiter has mapped the near and far side of the moon with exquisite detail. And China has just launched the robotic mission Chang & # 39; e 4, which will perform the very first landing on the other side of the Moon in early January. When humans finally return to the moon, the far side must be a landing goal. Understanding it will allow us to better understand not only the past of the moon, but perhaps its relationship to the Earth, our past.

This article was provided by the sister magazine, All About Space, from Space.com, a print magazine dedicated to astronomy, space exploration and the night sky. Sign up for the All About Space newsletter for information on news and subscriptions! follow us @Spacedotcom or Facebook. This version of the story published on Space.com.