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Useful Notes: The Moon
Kinda looks like Little Orphan Annie, doesn't it?

"But why, some say, the moon? Why choose this as our goal? And they may well ask why climb the highest mountain? Why, 35 years ago, fly the Atlantic? Why does Rice play Texas? We choose to go to the moon. We choose to go to the moon in this decade and do the other things, not because they are easy, but because they are hard!"
John F. Kennedy's "Address at Rice University on the Nation's Space Effort"

Earth's only — or at least, only significant — natural satellite.

It orbits our planet some 400,000 kilometers away, taking 27.3 days to go all the way around once. (Since the Earth will have moved some distance around the sun by the time the moon has orbited once, it takes a little longer — 29.5 days total, to be precise — for the lunar light-cycle to get back around to the same phase it started in.) Tidal forces long ago caused the moon to lock in synchronous rotation with the Earth, so that the same side is always facing us.

Compared to other moons in The Solar System, Earth's moon is really huge compared with the planet it orbits, weighing in at a whopping 1/81 of Earth's mass and 1/6 of Earth's surface gravity. By comparison, even the largest moon of Saturn is only 1/4000 of Saturn's mass. The Moon also has roughly 2/9 the mass of Mercury and is about 1.8 times more massive than all five recognized dwarf planets (Eris, Pluto, Makemake, Haumea, and Ceres), Pluto's satellite Charon (which is more massive than Ceres), and the Asteroid Belt (Ceres excluded) combined. Among the moons of Jupiter and Saturn, only Ganymede, Titan, Callisto, and Io are more massive than the Moon. Of them only Io is dense enough to have a higher surface gravity than the Moon.

Currently, our best guess at how such a humongous companion came into existence is that a Mars-sized planetessimal struck the Earth early in its formation period, which knocked loose a huge chunk of material that eventually cooled, congealed, and settled into the moon's current nearly-circular orbit. However, a recent comparison of the Earth-moon titanium isotope ratio has thrown this model into question.

The moon has been with us since before the dawn of the human race, progressing through its utterly predictable phases night after night. For most of human prehistory, it was the only light source available to us at night, which lent it a good deal of mystique. Lunar deities are almost as prevalent as Solar deities in mythology. The fact that the moon's 29-and-a-half-day light cycle is very similar in duration to the average woman's menstrual cycle has also not escaped the notice of poets, philosophers, and biologists; indeed the moon is often associated with femininity in literature and myth. However, there are more male lunar deities than female lunar deities. While Greeks and Romans considered the moon a woman, to the Germanic peoples it apparently was a man, which is how we get The Man in the Moon.

Loss of personal control and going berserk are also associated with the full moon, and not just when dealing with werewolves; the very word "lunatic" refers to the moon.

The moon is also the major cause of tides on the Earth. When the moon is directly above you or directly below you (i.e. on the opposite side of the Earth), tides are highest; when it's 90 degrees off to one side of you, tides are lowest. The Sun also causes tides, but these tides are much weaker than the moon's.

Sadly, the moon will not be with us forever. Those same tidal forces that pull on the Earth's oceans and locked the same face of the moon toward the Earth are also, very slowly, widening the moon's orbitnote . In a short time (on a geological scale, at least), the moon will be too far away to cause total solar eclipsesnote . Eventually, it will be enough to leave Earth orbit entirely, and wander through space just like in Space: 1999, though by the time that actually happens, the Sun would have expanded into a red giant and englufed the Earth already.

The moon's surface is covered in craters, caused by comet and asteroid impacts in the ancient (and, occasionally, recent) past. Each of those craters has a name, and most are named after scientists and philosophers. For instance, the great big crater with the huge white rays coming out of it in all directions is Tycho Crater, named after Tycho Brahe. The moon's surface is also partially covered by "Seas" (maria in Latin), dark areas where ancient volcanoes spilled lava all over the place. Like the craters, each Sea has a name, but unlike the craters the Sea names are derived from things that sailors might be concerned about — the Sea of Tranquility, the Sea of Rains, the Sea of Fecundity, etc..

Despite how bright the moon may appear in the night sky, its surface is very very dark. Its albedo is a dismal 7%, which means that 93% of all incident light is absorbed without being reflected back into space. For comparison, Earth's albedo is around 38%. The difference in color between the light-colored regolith and the dark-colored maria is like the difference between coal dust and extra-dark coal dust.

Since the moon keeps the same face pointed toward Earth at all times, the far side of the moon can't be seen from the Earth's surface, and it wasn't until the advent of the first space probes that we had any idea what the far side looked like. (It's got a lot less maria and a lot more craters than the near side; the slightly greater density of the dark maria material may be why the maria-rich side ended up facing Earth.) Both the near side and the far side wax and wane through light-and-dark phases, so it's incorrect to call the far side "The Dark Side of the Moon" except during the brief period every month while the moon appears Full in Earth's skies.

Examples with the moon as a place


  • A Trip to the Moon, the first movie to rely on special effects to tell the story of a trip, featured people getting shot to the moon inside a giant cannon shell — which gave the Man in the Moon a black eye.
  • In 2001: A Space Odyssey (written and premiered in the years prior to the Apollo landings) mankind has an established moonbase and space travel to the moon is a semi-mundane trip.

Comic Books
  • The Tintin graphic novel Explorers on the Moon features a surprisingly realistic take on what travelling to the moon would be like, despite being written pre-Sputnik.

  • H. G. Wells's The First Men in the Moon has its protagonist travel to the moon through the use of "cavorite", a magical Anti Gravity metal.
  • The Mouse on the Moon, the 3rd installment in the Mouse that Roared series, features the mini-country of Grand Fenwick embroiled in The Space Race with the Americans and Soviets. They get to the moon with a rocket powered by wine fermentation.
  • Jules Verne's From the Earth to the Moon has a huge bullet-like spacecraft shot off a cannon with three people in it. The book ends there, but the sequel, Around the Moon, deals with the space travel. However, they never reach the moon, only orbit around it and back (as the title implies).

Live-Action TV
  • Doctor Who 1966 story "The Moonbase" (set in 2070), has the Second Doctor visit a Moonbase that controls Earth's weather and stop the Cybermen (in their second appearance) taking over the Moonbase.


  • The Walter Koenig vehicle Moontrap involves alien intelligences lying in wait on the moon.
  • Apollo 13, being based on the Real Life Apollo moon mission, had the moon as the crew's ultimate (original) destination.
  • The film Moon takes place on the titular worldlet.
  • The opening of Independence Day features the alien mothership flying past the moon, so close that its gravity (or engine-emission vibrations, we can't really tell) disturbs the Apollo 11 landing site.
  • In Superman II, the escaped Krypton criminals land on the moon before they reach the Earth. Woe to the lunar astronauts who happened to be there at the time.
  • Apollo 18 is a fictionalized account of a top secret final moon landing, presented as a Found Footage Film.

Live-Action TV
  • Space: 1999 takes place on Moonbase Alpha in the far distant future year of 1999. A nuclear explosion on the moon's surface knocks it out of Earth orbit, sending it drifting through the galaxy rapidly enough to pass through a new star system every week.
  • The pilot episode of Salvage 1 features Andy Griffith managing a mission to the moon in a homemade rocket. (They can get away with this because their NASA reject friend has concocted a rocket fuel hundreds of times more efficient than anything the space program has yet put into production.) His intent is to salvage all the "junk" the Apollo astronauts left lying around on the moon and sell it.
  • The 1998 miniseries From the Earth to the Moon is about the race for the moon in the 1960's.

Video Games
  • This is the main battle ground in Asura's Wrath for the final fight between Asura and Augus, as well as the fights against Evil Ryu and Akuma/Oni.
  • Mass Effect 1 has a mission on the moon to stop a rogue military Virtual Intelligence (VI) which has taken over some defense and training systems.

EarthUsefulNotes/The Solar SystemMars
VenusUseful NotesMars

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