Meet The Moon - Earth's Cosmic Companion

At an an average of 238,855 miles (384,399 km) away from Earth, or about the space that could be occupied by 30 Earths, the moon is our closest neighbor in space, which is part of the reason it’s so visible and big. It orbits us while we orbit the Sun and is tidally locked to us so that we only see one side of it from here on Earth which waxes and wanes in eight phases over the course of 27.322 days.

Although it has been in our skies for longer than there have been humans to gaze up at it, America and the USSR began pushing for the moon during the space race with the first partial success with the USSR’s Luna 1 completing a flyby in January 1959. 

The first successful landing was in May 1966 by NASA’s Surveyor and on July 16, 1969, the first humans landed on the moon as part of NASA’s Apollo 11 mission. Since then, we have sent 12 men to the moon with the last being in 1972. However, NASA now plans to send the next people, including the first woman and person of color, back to the moon by 2025!

Since it’s only one step away and vitally tied to our planet’s past, present, and future, the Moon has been the subject of many different research missions delving into topics such as:

• How it formed in relation to Earth
• The viability of various human and technology-led initiatives on its surface and in its orbit
• The potential of using it as a future launching point for missions
• The potential of life to survive in inhumane environments
• The formation of moons and their relationship with their planets over time

Physical Characteristics

All in all, the Moon is about a quarter the size of Earth (and the fifth largest in the solar system). It’s about as wide as the U.S. or Europe. The moon’s volume is a little more than half of Earth’s and it’s about 60% as dense as Earth. The gravity of the moon is about 16.6% that of Earth’s.

What’s the surface like?

If we take a moment to observe it even with the naked eye, we easily spot dark areas and craters marring its surface. Every month we see it slowly increase in size until it is fully illuminated in the night sky and then slowly disappears again as it orbits around us. 

The moon is tidally locked, meaning it rotates at exactly the same rate as it orbits around us, and we only ever see one side of the Moon from Earth.

This familiar face of the Moon is mainly white with several darker areas, called maria. In ancient times, observers believed these darker areas were liquid water and therefore called them maria, Latin for seas. 

They are impact basins that were filled with lava between 4.2 and 1.2 billion years ago. The light areas are known as the highlands and represent rocks of different composition and ages than the marias. As a whole, the moon is covered with craters from impacts. 

Most of the Moon is covered by rubble of charcoal-gray powdery dust and rocky debris called regolith from the steady rain of impacts which were ground into fragments that quickly covered astronaut suits and are extremely abrasive.

What about its atmosphere?

Despite previous conclusions that the moon has no atmosphere, current data shows that the moon does have a very thin atmosphere – known as an exosphere – of helium, argon, neon, ammonia, methane, and carbon dioxide.

Is there a magnetic field?

No, the moon does not have a magnetic field.

Is there water?

Yes! Researchers have measured the presence of water in the form of ice within dust and minerals on and under the surface, primarily in areas that are in permanent shadow, meaning they stay very cold. This water was likely delivered by impacts from comets.

Days and Years on the Moon

While we’ve talked before about the length of a day and year on each planet a day is defined by the time it takes for the planet to turn around once on its axis and a year is defined as the time it takes for the planet to orbit the Sun. While it is about 24 hours per day and about 365.25 days a year on Earth, it is different in other worlds.

For the Moon, a day is 29.5 Earth days. This is because the Moon is tidally locked with the moon meaning it takes the same to orbit on its axis as it does to orbit around the Earth. This is also the length of the lunar cycle containing 8 phases we see from here on Earth.

Since the Moon orbits the Earth as the Earth orbits the Sun, a year is essentially the same on the Moon as it is on Earth.

Phases

Every month we see the moon slowly increase in size from the hidden new Moon and crescent Moon through the fat gibbous phase until it is fully illuminated in the night sky and then slowly disappears again as it orbits around us.

The 8 major phases are:

1. New Moon – This phase occurs when the Moon is between the Earth and the Sun, and the side of the Moon facing Earth is not illuminated by the Sun, making it invisible in the night sky.

2. Waxing Crescent – As the Moon moves in its orbit, a small sliver of the Moon becomes visible after the New Moon phase. This is the beginning of the waxing phase, where the illuminated portion of the Moon increases.

3. First Quarter – This phase occurs when the Moon has traveled about a quarter of the way around the Earth, and half of the Moon’s surface is illuminated.

4. Waxing Gibbous – The Moon continues to wax, and more than half of the visible side of the Moon is illuminated but it is not yet full.

5. Full Moon – The Moon is on the opposite side of the Earth from the Sun, and the entire face of the Moon that faces Earth is fully illuminated.

6. Waning Gibbous – After the Full Moon, the amount of illumination begins to decrease, meaning the Moon is waning. The waning gibbous phase is when there is more than half of the Moon’s face illuminated, but it is decreasing.

7. Last Quarter – Also known as the Third Quarter, half of the Moon’s surface is illuminated, similar to the First Quarter, but the opposite side is now visible.

8. Waning Crescent – The last phase of the Moon before it returns to New Moon, with a diminishing crescent of illumination.

For more information on each phase of the Moon, check out our previous article on the lunar cycle.

Formation and Geology

How did the Moon form?

The moon formed about 4.5 billion years ago when a Mars-sized object we’ve dubbed “Theia” crashed into Earth during the chaotic early formation of the planetary bodies of the solar system.

Some of the debris from this impact was flung out into space, but was close enough to be caught in the New Earth’s gravity. This debris quickly (potentially in as little as hours) merged into a single object which then slowly cooled into what we see as the Moon today.

The Moon Over Time

Data suggests the Moon was once a great ocean of magma due to its formation as the leftovers of an interplanetary collision, with dense minerals sinking to the bottom and lighter minerals rising to the surface to form the crust. 

As the Moon formed, heavier materials sunk into the core while lighter materials stayed in the outer layers called the crusts. As a result, the Moon is made up of different layers, each with its own unique composition. 

Scientists have used various methods, like measuring earthquakes and the Moon’s spin and gravity, to figure out what’s inside.

What is inside the Moon? Is it similar to Earth?

The Moon is a rocky body with a combination of metallic substances in the layers of its surface. It is mainly made of iron, but other metals can be found on its surface, including aluminum, magnesium, titanium, silicon, silver, gold, and mercury.

The core of the Moon is its densest layer, mostly made of iron and nickel, with a solid inner core of 480 km diameter and a fluid outer core of 660 km diameter. It is relatively small at only about 20% of the Moon’s diameter compared to other terrestrial worlds.

The mantle and crust, also known as the lithosphere, make up the rest of the Moon, with the mantle being roughly 1350 km thick and the crust around 50 km, but the thickness of the crust varies, with the side facing Earth being thinner and the side facing away being thicker, but we are still researching why this is the case.

Interesting Topography

There are many interesting places on the Lunar surface, primarily grouped into plains and maria as well as interesting geologic formations, and craters.

Some include:

• Tycho Crater: appears as a bright spot in the southern highlands with rays of bright material, stretching across much of the near side of the moon; while it is large at 85 km in diameter, it is one of thousands that big, but it is important because it’s a relatively young crater
• Marius Hills Lava Tube Pit: 190 feet (58 meters) in diameter and 131 feet (40 meters) deep, this pit was discovered in images from the Kaguya orbiter and could be the opening to a large lava tube complex under the surface; these volcanic features help scientist understand the volcanism in the Moon’s early history and may be crucial to human habitation on the Moon as they could offer protection from harmful radiation, meteorite impacts, and the extreme temperature differences
• Linne Crater: a beautifully preserved young crater, potentially less than 10 million years old, with no signs of any subsequent major impacts and retaining its original shape
• Schrödinger Basin: one of the youngest basins on the lunar surface with pyroclastic deposits of valuable metals such as iron and titanium at the south pole
• South Pole-Aitken Basin: the largest and oldest recognized impact basin with a diameter of about 1,550 miles (2,500 kilometers), meaning it stretches across nearly a quart of the Moon, on the far side of the moon
• Apollo Basin: a double-ringed impact crater in the southern hemisphere of the far side; many craters within it are named after deceased NASA astronauts and officials, including the fallen crew of the Space Shuttle Columbia
• Van De Graaf Crater: a merged crater that is distinctive, because there is no rim separating the two sections and since a relatively strong magnetic field was detected near it
• Tsiolkovskiy Crater: Discovered by the USSR’s Luna 3 which took the first images of the never-before-seen dark side of the moon (where this crater lies); named for Konstantin Tsiolkovsky, one of the fathers of modern rocketry
• Stratton: Named for British astrophysicist Frederick J.M. Stratton, this area on the far side is of scientific interest for a high concentration of iron
• King Crater: one of the youngest craters on the far side, known for its remarkable claw-shaped central peak and an unusually large melt pond
• Many shapes on the Moon’s surface thanks to the light and dark areas visible with the naked eye: Rabbit, Man in the Moon, and the soccer player.

Can I explore these features and the moon’s surface in general?

Absolutely! There are many interactive programs and resources to explore the moon including:

• NASA Eyes on the Solar System: Moon of Earth
• The Starlust Lunar Landing Site Map
• Lunar and Planetary Institute (LPI) Lunar Map Catalog
• NASA Moon Map
• Google Moon (like Google Maps but fo the Moon!)

Climate

Temperatures

With only a very thin atmosphere, the Moon can’t hold onto heat and therefore temperatures fluctuate drastically depending on whether the surface is in the daytime or nighttime, similar to Mercury. Daytime temperatures near the Moon’s equator reach 250 degrees Fahrenheit (120° C, 400 K) while nighttime temperatures drop to -208 degrees Fahrenheit (-130° C, 140 K).

Weather

Since the Moon does not have a significant atmosphere, it does not experience weather in terms of wind or precipitation like rain and snow.

However, it does experience what is called space weather including solar wind composed of charged particles from the Sun that shoot out in flares and more frequent meteoroid streams since they can’t burn up like they do in our atmosphere (which is one of the reasons why the Moon has so many craters). In fact, both solar wind and meteoroid impacts alter both the surface and eject gases from the soil, creating the tiny exosphere.

Seasons

Seasons on Earth are due to the tilt of the Earth’s axis (at about 23.5 degrees) meaning the intensity of sunlight that reaches various regions of Earth changes throughout the year, creating periods that are hotter or colder versus other regions on the other side of the world.

The Moon’s axis is tilted by only about 1.5 degrees, meaning it doesn’t experience noticeable seasons.

Exploration of the Moon

The Moon has been extensively studied. From visual observations dating back thousands of years to the telescope bringing its features into closer view and now with over 50 spacecraft (including 19 landers and 6 rovers) have successfully launched to fly past, orbit, impact, and land on the moon, we know our neighbor pretty well.

Below is a table of the manned missions to the moon as of May 2023:

Note: Apollo 13 was deemed a “successful failure” when an oxygen tank blew, causing damage to the other oxygen tank as well as damaged electric and other life support systems. The crew eventually had to escape in the Lunar Module and make their way back to Earth. 

While the mission was a failure, the crew and NASA learned invaluable lessons in how to get the crew back home safely in the event of a failure.

In addition, below are a few of the notable unmanned missions, ranging from the early days of the space race to the present times. 

This is not an exhaustive list for which I would recommend NASA’s Moon Missions page and this related Moon Missions and Data Page.

NASA’s ongoing Artemis missions are focusing on sending humans back to the moon for good in preparation for sending humans to Mars. The future missions will include installing a lunar base and a space station in orbit around the moon known as Gateway. The next few years will be particularly exciting as the first landing is scheduled for 2024.

The Moon in Popular Culture

The moon is the most referenced astronomical object in pop culture as it is the brightest and largest object in the night sky except around the New Moon phase. Since it has been humanity’s constant companion, it has been interwoven into human culture including mythology, music, language, and other forms of entertainment over thousands of years.

Entire books can and have been written on the moon’s impact on various areas of culture. Below are some of the most prominent examples. As a whole the Moon is often seen as a feminine symbol, deity, etc. denoting love (and lovesickness), as well as part of the dualism of life and death, night and day, etc.

As we have explored more of the Moon, first with the telescope and then with spacecraft, these findings impacted the moon’s depiction in popular culture, delving into ideas of first voyages, colonization, and long-term habitation.

The Moon in Mythology

Every culture has depicted the moon within its cultural mythology and legends in various ways though documentation varies, with Greek and Roman versions being the most well-known today due to colonialization. There are many deities of the Moon or associated with the Moon in a variety of ways.

Chinese mythology, for example, includes Jie Lin, the god that carries the Moon across the night sky; Chang Xi, the mother of twelve moons corresponding to the 12 months of the year; Chang’e, an immortal that lives on the moon (and the name of the Chinese Lunar Exploration Program); Tu’er Ye, a rabbit god that lives on the Moon; and Wu Gang, an immortal that lives on the Moon.

Khonsu is the Egyptian god of the Moon who thanks to losing a game of senet, gave away moonlight to create 5 additional days for Nut the Sky goddess to give birth to her children. The Greek goddess is often associated with the moon as the sister to Apollo, the Sun God, but Selene is the official Greek goddess and personification of the Moon.

Diana is the Roman goddess of various objects and people as well as the Moon. Her mythology was equated and mixed with Artemis and Selene across cultures. Hecate in Greek mythology is often associated with the Moon, but is not an official goddess of the Moon. Luna is the Roman counterpart to Selene and sibling to Sol and Aurora (goddess of dawn).

In Norse mythology, Máni is the personification of the Moon and brother of the personified Sun, Sól. Aztec mythology featured at least three deities for the Moon: Metztli (male or female), Coyolxauhqui (female), and Tecciztecatl the Man in the Moon. A Japanese folktale tells of a Moon princess growing up on Earth as the adopted daughter of a bamboo cutter and his wife.

The Moon in Literature

The Moon has been featured extensively in literature for thousands of years in poetry, romance, legends, and more. Fairy tales, folklore, and children’s stories have featured the moon essentially since the beginning as well as odd retellings such as The Princess of the Moon: A Confederate Fairy Story (1869) where a fairy of the Moon saves a Confederate soldier.

There are also literary examples of imaginary voyages to the Moon as far back as at least the 2nd century AD with Lucian’s Icaromenippus and True History (of outlandish tales) and one of the earliest fictional flights to the Moon is in Ludovico Ariosto’s well-known Italian epic poem Orlando Furioso (1516).

Science Fiction has produced numerous novels, short stories, and more featuring and centering on the Moon including:

• Jules Verne featured the Moon in some of his most well-known works including his 1865 novel From the Earth to the Moon and its sequel which used a similar voyage to how the Apollo program lunar orbit rendezvous ended up happening.
• H.G. Wells also featured the moon in his works including The First Men in the Moon in 1901.
• Robert A. Heinlein wrote extensively on the Moon, which he often called Luna, featuring over a dozen pieces centered on our celestial neighbor
• The Lathe of Heaven (1971) by Ursula Le Guin
• The Gods Themselves (1973) by Isaac Asimov
• 2001: A Space Odyssey Arthur C. Clarke
• Artemis (2017) by Andy Weir who wrote The Martian

J.R.R. Tolkien not only pulled from Norse and Gaelic lunar mythos for the fictional Middle-Earth cosmology (the world of The Lord of the Rings, etc.) but also created a children’s story called Roverandom about a dog flying to the Moon and his adventures there as well as an original song “The Man in the Moon Stayed Up Too Late” which is based on the 16th century “Hey Diddle Diddle the Cat and the Fiddle… the cow jumped over the moon” nursery rhyme.

“Goodnight Moon” by Margaret Wise Brown (1947) is one of the most well-known and still used children’s bedtime stories.

The Moon in TV, Film, Radio, Theater

As storytelling changed, the Moon continued to be featured, again in too many examples to list here.

In the Theater:

• Il Mondo della Luna was 1777 opera and Frau Luna was an 1899 operatta.
• The End of the Moon by Laurie Anderson is a 90-minute monologue created as part of Anderson’s two years as NASA artist-in-residence (2005)

In film:

• A Trip to the Moon (French: Le voyage dans la lune) is the famous 1902 French silent film by Georges Méliès inspired from a wide variety of sources including Jules Verne’s 1865 From the Earth to the Moon and its sequel. It is most known for the scene/ image of a bullet-shaped spaceship smashing into the moon which seems to have a face.
• Woman on the Moon (1929): considered the first-ever space blockbuster
• 2001: A Space Odyssey (1968)
• The Right Stuff (1983) about the early space program
• Apollo 13 (1995) about the historic mission
• Space Cowboys (2000)
• The Adventures of Pluto Nash (2002)
• Moon (2009) about a lunar miner
• First Man (2018) about Neil Armstrong and the race to the moon

In TV:

• Men Into Space: sci-fi TV series about the US Air Force’s efforts to send American astronauts into space, particularly the Moon
• Doctor Who: various episodes and arcs including the 1967 (pre-moon landing) 4 part serial The Moonbase set in the year 2070 and the Frontier in Space serial (1973)
• For All Mankind (2019- present): an alternate reality where the Soviet Union beats us to the moon
• Moonhaven (2022): a dystopian show about a lunar colony
• Moonbase 3 ( 1973): British television show about a lunar base
• Space Brothers: a Japanese anime of two brothers becoming astronauts

The Moon in Comics

The Moon has been frequently featured as a setting in comics for decades, often briefly and sometimes more substantially. A few examples are below.

• Ibis the Invincible: the Moon has members of a humanoid race composed of stone that were exiled to the Moon after their war over Earth
• The Adventures of Nero: 1968 “De Paarse Futen” story including astronauts who went to the Moon
• In the Marvel Universe: the Moon contains the Blue Area, home of the Inhumans; the powerful Watcher Uatu watches the Solar System from a Moon base; the Fantastic Four make the first landing on the Moon (published before the actual moon landing); popular character known as Moon Knight
• In the DC Universe: the Moon is the location of the Justice League Watchtower

The Moon in Video Games

Video games that feature celestial locations often feature the moon. Below are a few.

• Kerbal Space Program is an educational space simulation game that features a goal to visit and plant their flag on the Moon
• Ragozin on Moon is a family-friendly survival game set on the Moon
• Lunistice is an adventure game with the final destination being the Moon
• Moon Runner: a survival shooter video game set on the Moon
• Deliver Us The Moon is a short sci-fi game set on the Moon
• Destiny features the Moon as a setting
• Super Mario Odyssey includes levels on the Moon
• DuckTales also has a moon-level
• Command and Conquer 2: Yuri’s Revenge: players are tasked with taking down Yuri Gagarin’s (the first man in space) secret lunar base in the Sea of Tranquility
• Wolfenstein: The New Order takes place on the Moon

The Moon in Music

The Moon has featured heavily in music for thousands of years, but here are a few modern examples.

• “Moondance” by Van Morrison
• “Fly Me to the Moon” by Frank Sinatra
• “Talking to the Moon” by Bruno Mars
• “Song About the Moon” by Paul Simon
• “Moon At the Window” by Joni Mitchell
• “Mr. Moonlight” by the Beatles
• “Moon Is Up” by the Rolling Stones
• “Whitey On The Moon” by Gil Scott-Heron
• “The Moon is a Harsh Mistress” by Glen Campbell
• “Walking On the Moon” by The Police
• “Man on the Moon” by R.E.M.
• “Blue Moon of Kentucky” by Elvis Presley
• “Moonshadow” by Cat Steven”
• “Moon River” by Sarah Vaughn
• “Bad Moon Rising” by Creedence Clearwater Revival
• “Blue Moon” by Billie Holiday
• “Rocket Man (I THink It’s Going To Be A Long, Long Time)” by Elton John (inspired by the Moon landing and a Ray Bradbury short story)
• “Space Oddity” by David Bowie (rushed out as a single five days before the Apollo 11 launch)
• The Dark Side of the Moon album by Pink Floyd
• Swingin’ On the Moon album of moon songs by Mel Tormé
• “Moon,” a solo track by Jin, featured on BTS’ 2020 studio album Map of the Soul: 7. Jin assumes the perspective of the Moon, circling and being perpetually watchful of the Earth

The Moon in language

Moon comes from the old English “mōna” of Germanic origin and can be traced back further to the Proto-Germanic word “mēnô.” These Germanic languages, in turn, have cognates in other Indo-European languages, such as the German “Mond” and the Dutch “maan” reflecting the ancient cultural significance of the moon. It is also related to “month”, from an Indo-European root shared by Latin mensis and Greek mēn ‘month’, and also Latin metiri ‘to measure’ (the moon being used to measure time).

The term “lunar,” derived from the Latin word “lūna,” relates specifically to the moon and its phases. Words like “lunatic” or “lunacy” (and the idea that people are more erratic around the full moon) and “lunation” are derived from “lūna” and pertain to the moon or its cycles. The etymology of “moon” and its related words showcase the enduring fascination and influence of Earth’s natural satellite on human language and culture throughout history.

Observing the Moon in the Night Sky

The moon is the brightest object in the night sky due to its close proximity to Earth and can even be seen during the daytime sometimes. You don’t need any equipment to view the Moon, but binoculars or a small telescope can bring some of its features into brilliant resolution. Just make sure you are using a moon filter as the moonlight is very bright, especially for long periods of observation at higher resolutions.

A great first step to observing the Moon is simply keeping a moon observation journal. Go out every night and keep track of what phase it is in, what features you see, etc. Again, even with the naked eye, you will be able to glean wonderful information about the moon, especially with frequent observations. 

From New Moon to Full Moon and every phase in between, you will be able to greater appreciate the Moon with a little observation. Every year, you can participate in the International Observe the Moon Night, usually around the full moon in October or the third Saturday. For 2023, it was October 21st.

Eclipses

Eclipses occur when one astronomical body appears to cover another body from the observation of a third body. In this case, we see the Moon appear to cover the Sun from our perspective here on Earth or see the effect of the Earth covering the Sun on the Moon.

During a solar eclipse, the Moon appears to cover up the Sun. Solar eclipses happen at the New Moon phase when the Moon is directly between the Sun and the Earth, but doubly so. Normally, during the New Moon phase, the moon simply disappears as we “see” its nighttime side.

However, when the orbits line up exactly, the moon crosses directly across the Sun, covering it and casting a shadow across the Earth, blocking or partially blocking our view of the Sun. Solar eclipses are only visible within this shadow (only about 300 miles or 480 km wide) and therefore cover a small area of Earth, often over the ocean, making it rarer to observe one unless you schedule it ahead of time.

In contrast, a lunar eclipse occurs when the Earth is perfectly between the sun and the moon at full moon phase and the Earth’s shadow falls across the face of the Moon. There are three types of lunar eclipses, depending on how far the moon moves into the Earth’s shadow, but the most dramatic is the Total lunar eclipse (a.k.a. a Blood Moon) when a full Moon is completely blocked from the Sun’s rays by Earth’s shadow.

For more information on eclipses, check out our solar vs. lunar eclipse guide.

Summary and Future Prospects

The Moon holds immense importance in both scientific and cultural realms. Scientifically, it plays a pivotal role in Earth’s stability and evolution, regulating tides through gravitational forces and possibly impacting our climate.

Understanding the intricate relationship between Earth and the moon has deepened our comprehension of planetary dynamics and celestial mechanics. Culturally, the moon has been a source of inspiration, symbolism, and myth across the ages, influencing art, literature, and other areas of popular culture.

It has been a symbol of beauty and mystery, and its phases have been woven into human calendars and traditions. Looking to the future, the moon remains a focal point of exploration and potential colonization, serving as a stepping stone for human ventures into deeper space including Mars.

Lunar exploration offers valuable insights into the history of our solar system and may even hold the key to sustainable space habitats, fueling aspirations of a multi-planetary future for humanity.

Fun Facts About the Moon

1. Our Moon is the second densest moon (the first is Io of Jupiter).
2. While it appears bright compared to the night sky, the Moon’s surface is actually dark, with a reflectance just slighter higher than worn asphalt.
3. The Moon did not always eclipse the Sun and will not always continue to do so! It started much closer to the Earth and has been slowly drifting outward at about 1.5 inches (3.8 cm) per year. In about 600 million years, it will move far enough away for eclipses to occur.
4. The Moon makes not only the oceans move with the tides, but the whole Earth! It’s not nearly as dramatic as the tides, but the solid surface of the Earth moves by several centimeters with each tide.
5. The moon has quakes too, called moonquakes instead of earthquakes, caused by the gravitational influence of the Earth. They last longer than most earthquakes but are much weaker.