The Earth revolves around the Sun every 365 ¼ days, and rotates on its axis every 24 hours. The Moon revolves around the Earth every 27 days, and it rotates on its axis the same time, every 27 days. Because the two are synchronized, people on Earth look up at one surface of the Moon, the near side.
Each side of the Moon though, near or far, receives sunlight for two weeks.
The near or visible side of the Earth, seen at night, is composed of flat plains called seas, of highlands called mountains, and of craters, but the Moon’s far side is littered with a bewildering numbers of craters, each given a name, but no seas.
Earth’s Moon is the fifth largest of all the Solar System’s moons, but it is the largest relative to its planet, about 27 ½% the size of Earth. Earth and Moon coordinate with each other during their annual elliptical path around the Sun.
NASA has deployed at least three series of probes to the Moon: Ranger, Surveyor, and Apollo.
Of the nine Ranger probes, in the early 1960s, three succeeded in sending back a total of 17,439 pictures of the Moon, minutes before each hard-crashed into the Moon’s surface.
Of the seven Surveyor probes, in the mid-1960s, two crash-landed, but five soft-landed on the Moon’s surface, and then sent back pictures of the Moon’s surface. All seven still remain on the Moon.
Of the fifteen Apollo missions in the late 1960s, six soft-landed on the Moon’s surface: 11, 12, 14, 15, 16, and 17. The twelve Americans who walked on the Moon’s surface plus the other six who remained inside the Command Modules in lunar orbit returned to Earth.
The Moon’s near side is defined by x / y coordinates, with a center point at 0 degrees latitude, 0 degrees longitude.
On July 20, 1969, Apollo 11’s astronauts, Neil Armstrong and Edwin “Buzz” Aldrin, landed their Lunar Module, the Eagle, onto the Sea of Tranquility’s southern edge, about 500 miles due east of the center point, close to where Ranger 8 and Surveyor 5 had landed earlier.
On Nov. 15, 1969, Apollo 12’s astronauts, Charles Conrad, Jr., and Alan L. Bean, landed their Lunar Module, about 500 miles due west of that center point, on the eastern edge of Oceanus Procellarum, or the Ocean of Storms, but only 600 feet from Surveyor 3.
Conrad and Bean walked to that previous Moon probe, that had soft-landed on April 20, 1967, nineteen months before, and investigated it, even snapping a photograph of it and themselves.
Apollo 14 landed about 400 miles west of the center point. Apollo 15 landed about 700 miles due north of the center point, about 40 percent of the distance to the Moon’s north pole. Apollo 16 landed about 500 miles south and east of the center point. Apollo 17 landed about 800 miles north east of the center point.
One can see that NASA’s moon landings in the 1960s and 1970s clustered about that center point. Only one of its moon landings—from either Ranger, Surveyor, or Apollo—touched down on the Moon’s far side, Ranger 4, on April 26, 1962, and that was due to a malfunction.
Other countries have sent probes to the Moon, including: the Soviet Union and / or Russia, Japan, China, the European Space Agency, India, and now Israel.
On Jan. 3, 2019, China’s National Space Administration Agency soft-landed “Chang’e 4” on the Moon’s far side, inside the Van Karman crater, almost 1,000 miles due south of that side’s center point, 60 percent of the distance to the Moon’s south pole.
The Van Karman crater lies within a vast basin, a depressed area on the Moon’s far side, called the South Pole-Aitken Basin, one of the largest impact basin’s in the Solar System, 1600 miles in diameter and eight miles deep.
Last month, Peters B. James, a professor of planetary geophysics at Baylor University, announced that he and his team had discovered “a mysterious large mass of material beneath the Moon’s South Pole-Aitken Basin, and that it may contain metal from the asteroid that crashed into the Moon and that formed the basin.” It lies at least five miles and more below the Moon’s surface.
The Israeli’s attempted to send a recent un-crewed probe to the Moon’s surface. Called Beresheet, Israeli officials hoped to land it in the Sea of Serenitatis, just north of the Sea of Tranquility. On April 11, 2019, during its descent the spacecraft’s main engine stopped working, causing a hard-landing.
Moon exploration, a series of failures, but also a series of stunning successes.
