The moon, being our closest celestial neighbor, has been subject to critical observation or scrutiny over the years. It was formed some 4.5 million years ago, about 60 million years after the solar system itself. It is the only natural satellite revolving the planet Earth.
In the last five decades, a vast amount of research has been done regarding the moon’s formation, geology, composition, and its effects on the Earth, among other things. Keeping those studies into account, we have compiled a list of most interesting facts about the moon.
Equatorial Radius: 1738.1 km
Surface Gravity: 1.62 m/s2
Escape Velocity: 2.38 km/s
Mean Surface Temperature: -53.15 (at the equator)
1. The moon is also known by other names such as ‘Luna’ (Latin) and ‘Selene’ (Greek).
2. The term lunatic or lunacy (usually referring to a mentally ill), is derived from the Latin word for the moon, Luna. Since the time of the ancient Greeks, a widespread belief regarding the full moon is that it induces insanity in weakened individuals, causes traffic accidents and suicides. These beliefs have been debunked repeatedly.
Image Courtesy: Wikimedia Commons
3. The moon’s rotation on its axis is synchronized with its orbit around the Earth (shown on the left), resulting in tidal locking with one side of the moon always facing the planet. A scenario in which the moon is not rotating on its axis is shown on the right.
4. During a total solar eclipse, the moon nearly covers the entire Sun. That’s because the Sun is about 400 times the lunar distance from the Earth and has the same apparent size.
5. According to an estimate, there are about 300,000 impact craters on the near side of the moon.
6. The amount of artificial or human-made objects on the moon collectively weighs over 191,000 kg. It includes crashed probes and rovers that are out of commission.
7. In 2007, the X Prize Foundation, in partnership with Google, launched the Google Lunar X Prize competition. Prize money of $20 million was to be given to the first private aerospace company that would send a robotic lander on the moon by 2018. The competition ended with no winners.
Photograph of moon’s far side taken by Luna 3
8. The first-ever image of the moon’s far side (that always faces away from the Earth) was made by Soviet spacecraft Luna 3 on October 7, 1959.
9. The first human-made object to reach the moon’s surface was a Soviet lunar impactor, Luna 2, in September 1959.
10. We Can Observe About 59% of The Lunar Surface
Since one hemisphere of the moon always faces the Earth, it’s only logical that only half or 50 percent of the moon’s surface should be visible. However, due to a phenomenon known as lunar libration (wavering motion of the moon due to various factors), it is possible to see about 59 percent of the lunar surface for Earthbound observers.
11. It Is The Fifth Largest Natural Satellite In Our Solar System
Full moon | Image Courtesy: Gregory H. Revera
Our solar system contains about 205 natural satellites, most of which are irregular moons. Apart from Mercury and Venus, all the planets have natural satellites. The largest and most massive of them is Jupiter’s Ganymede. It is also the only natural satellite to have a magnetic field.
After Ganymede, the next largest moon is Saturn’s Titan, followed by Jupiter’s Callisto, and Io. With a diameter of 2,158 miles, the Earth’s moon comes in fifth.
12. It Has The Second Largest Confirmed Impact Crater In The Solar System
One of the moon’s most prominent geological features is a 2,500 km wide and about 8 km deep impact crater on its far side. The impact crater, known as the South Pole-Aitken basin, is the oldest and deepest basin discovered yet. It is also the second-largest confirmed crater basin in the solar system, after Mars’ Utopia.
The South Pole-Aitkin basin was discovered in the mid-1960s. However, not much was known about the crater until the 1990s. Recently, scientists have discovered a huge mass, possibly of foreign origin, buried deep inside the basin.
13. The Moon Is Shrinking, And It’s Causing Moon-quakes
According to data retrieved by the Lunar Reconnaissance Orbiter, the moon has shrunken by 50 meters over the last few million years. The moon’s shrinking is caused by gradual cooling of its interior, and it is evident by newly formed “thrust faults” on the lunar surface. An appropriate analogy of the phenomenon would be the shrinking of grapes into raisins. As a grape shrinks, it gets wrinkles. Many of these thrust faults or fault scraps are young and causing moonquakes.
The planet Mercury is also going through similar shrinkage. According to a study, the fiery world has shrunken at least 11 km since its birth, 4.5 billion years ago.
14. The Dark Spots On The Moon’s Surface Are Called ‘Maria’
A cylindrical map projection of the moon showing its global albedo from the Clementine mission. The dark regions are lunar maria
The dark spots visible throughout the moon’s surface are, in fact, vast pools of basaltic lava. They are called ‘maria’ – a Latin word for “seas.” Lunar basalt has more iron content than the terrestrial basalt and is less reflective, thus appear dark to the naked eye.
Most maria are located on the near side of the moon (the side visible from the Earth) and cover nearly 16 percent of its total surface. According to radiometric dating, the youngest lunar mare is estimated to be 1.2 billion years old. A majority of them formed between 3 billion to 3.5 billion years ago.
The largest known maria, known as Oceanus Procellarum, is located on the western side of the moon’s near side and covers about 4,000,000 km2 area.
15. It Once Had Magnetic Field Strength Similar To That Of The Earth
The moon has an extremely weak magnetic field compared to that of the Earth and is believed to be less than 0.2 nanoteslas. This due to the absence of an active dynamo (the source of magnetic fields on Earth and other planets). Whatever magnetic field strength we observe on the moon is caused by a phenomenon known as crustal magnetization (magnetic field of the crust).
However, it was not always the case. Research has shown that the moon once had a strong magnetic field, identical to the Earth’s, early in its life about 4 billion years ago.
Apparently, the moon lost most of its magnetic field strength approximately one billion years ago, when the core went cold and became crystallized.
16. Moon Had A Thicker Atmosphere In The Past
The moon possessed a thicker atmosphere in the past. Back in 2017, researchers at the Lunar and Planetary Institute and the Marshall Space Flight Center reported that in the past, about 3 and 4 billion years ago, the moon’s atmosphere was twice as much thick as that of the present-day Mars.
The moon’s thick atmosphere, in the past, is believed to be caused by the frequent discharge of gasses during volcanic eruptions, and it lasted for about 70 million years before it dissipated into space. The study is based on the Lunar magma data gathered by the Apollo missions.
17. The Solar System’s Coldest Place Is On The Moon
The dwarf planet Pluto, with a surface temperature of -240 degrees C, is widely considered as the coldest place in the solar system. However, that is not the case anymore.
While examining the data retrieved from LRO’s DIVINER instrument (an infrared radiometer for analyzing temperature differences on Lunar surface), in 2009, researchers discovered that temperature inside one of the craters (Hermite) near the north pole region of the moon could fall as low as -274 degrees Celsius during night time.
The study also revealed a few other craters near the region with almost identical temperatures.
18. It is Drifting Away From The Earth
Shortly after its formation, the moon’s distance from the Earth is believed to around 22,500 km. Fast forward 4.5 billion years in the present, that distance has increased to 384,400 km (average). Evidently, the moon is slowly drifting away from our planet. The rate at which it is occurring is close to 4 cm a year.
The rate at which the moon is moving away from the earth may seem insignificant for now. But over a long period, it could have devastating effects on the earth-moon system.
19. There Have Been No Manned Missions On The Moon Since 1972
The final crew of Apollo 17. Eugene Cernan (seated), Ronald Evans (on the right) and Harrison Schmitt (on the left) | Image Courtesy: NASA
Between the year 1969 and 1972, under the legendary Apollo program, NASA performed six successful crewed lunar landings. The United States remains the only nation in the world that has managed to achieve such a feat.
The last moon landing mission of the Apollo program, Apollo 17, itself, was record-breaking in various aspects. The Apollo 17 crew of Eugene Cernan and Harrison Schmitt spent the most time on the moon (over three days), performed the longest total moonwalk, and spent the longest time in the lunar orbit to date. The lunar samples gathered during the mission is the largest (by total mass) of all Apollo missions.
For more than four decades, after the completion of the Apollo 17 mission, no crewed landings on the lunar surface have either carried or planned. However, it is likely to change soon.
In May 2019, it was announced that under the Artemis program, NASA would carry out the next crewed lunar exploration by 2024.
20. The U.S Air Force Considered Detonating A Nuclear Bomb On The Moon
After the early success of the Soviets during the Space Race in the late 1950s, the U.S armed forces largely believed that a show of force (of such magnitude) is necessary to raise the morale of the American population. Another reason behind such an ambitious project was a circulating rumor that the Soviets were planning to detonate a hydrogen bomb on the moon.
Anyhow, Project A119 was canceled without any meaningful progress, mainly out of fear of adverse public reaction and a possibility of a major nuclear accident on the Earth.
The top-secret project was revealed in public for the first time in 2000 by a former NASA executive, who led the project in 1958.
Timeline of Lunar Exploration
Year 1959: On September 13, 1959, Luna 2 became the first human-made object to reach (hard landing) the lunar surface. Almost a month later, on October 6, Luna 3 took very first images of the moon’s far side from a spacecraft. Both missions were part of the Soviet Union’s Luna program.
Year 1966: The first spacecraft to make a successful soft landing on the moon’s surface was Luna 9 on February 3, 1966. It was the first on an extraterrestrial body. Then in early March, Luna 10 became the first space probe to successfully enter and maintain an orbit around the moon.
NASA’s Surveyor Model (on Earth)
NASA and America had no significant breakthroughs in early lunar exploration until June 1966, when Surveyor 1 made a successful soft-landing on the lunar surface. Then in August, the Lunar Orbiter 1 became the first American and only the second human-made satellite to orbit the moon.
Year 1969: On July 20, 1969, the Apollo Lunar Module ‘Eagle,’ carrying two American crew members (Neil Armstrong and Buzz Aldrin), successfully landed on the moon. It was the first and only manned space mission carried on a celestial body.
The landing was part of the legendary Apollo 11 mission that virtually ended the Space Race between the Soviet Union and the United States.
A photograph of Buzz Aldrin by Neil Armstrong on the Moon
The Apollo 11 mission was soon followed by Apollo 12, the second successful crewed lunar landing out of the total six to date. One of the mission’s main objectives was to bring back a few components of the Surveyor 3 robotic probe, which landed on the moon two years prior. It was the first and only instance when humans had revisited a probe on another celestial body.
Year 1970: The Soviet Space Program achieved a remarkable feat with Luna 16 and Luna 17 missions. In September 1970, the robotic space probe Luna 16 completed the first fully automatic retrieval of samples from the lunar surface. A small quantity of that sample was sold for US$855,000 in 2018.
On November 10, 1970, Lunokhod 1 became the first-ever robotic (fully autonomous) rover to operate on the lunar surface. It was the first wheeled craft to freely navigate on a celestial body other than the Earth. The rover was carried by the Luna 17 spacecraft.
The Apollo program ended with the completion of Apollo 17 in 1972. Since then, several crucial lunar missions have been conducted. Some of the most important them are Clementine in 1994-95, SMART-1 (ESA) in 2004, and Lunar Reconnaissance Orbiter in 2009.