How Many Moons Does Earth Have?

While other planets in our solar system boast multiple moons, Earth stands out from the pack with its singular celestial companion. Don t let that lonely number fool you, however. While Earth might not have over 100 moons like Saturn (or even two moons like Mars), our one and only Moon is nonetheless significant. From its unique characteristics to its global significance to its sheer beauty, there s truly no moon like Earth s. Let s take a brief look back at its history.

Specifications of the Moon

Designation	Earth I
Sidereal Orbital Period	27 days, 7 hours, 43 minutes, 11.5 seconds
Synodic Orbital Period	29 days, 12 hours, 44 minutes, 2.9 seconds
Orbital Speed	1.022 kilometers per second
Radius	1,737.5 kilometers
Circumference	10,921 kilometers
Estimated Age	4.5 billion years old
Distance From Earth	384,472 kilometers

5 Must-Know Facts About Earth s Moon

• The Moon is the fifth-largest natural satellite in the Solar System. However, it s significantly smaller than Earth, with a diameter about one-fourth the size of ours.
• Contrary to what humans used to think, the Moon doesn t produce its light. Instead, it reflects light from the Sun. As it orbits Earth, different parts of the Moon become illuminated. This causes the Moon s various phases: new moon, crescent moon, half moon, gibbous moon, and full moon.
• The craters that cover the Moon are the result of meteoroids, asteroids, or comets colliding with the surface. The Moon used to have many active volcanoes, which also contributed to the craters on its surface.
• The Moon s gravitational pull causes the oceans to bulge outward, creating high tides. As Earth rotates, different parts experience high and low tides throughout the day. This tidal interaction has been gradually slowing Earth s rotation over millions of years.
• Unlike Earth, the Moon has no atmosphere. This means the Moon has no breathable air, no protection from the harmful radiation of space, and no deterrent for incoming meteoroids. Consequently, there s also no weather on the Moon.

Origins of Earth s Moon

While there s no way to know for certain, the prevailing theory about Earth s lone moon is that it originated 50 million years after the formation of the Solar System. There are a few different hypotheses about the Moon s origin, each with its fair share of credible evidence. However, the giant impact theory is the most one accepted by most.

In this theory, scientists argue that Theia an ancient planet hypothesized as part of the early Solar System crashed into the Earth 4.5 billion years ago. As the theory goes, Theia and Earth s cores and mantles fused while the resulting debris formed the Moon. Scientists back this theory with evidence that Earth s core is much larger than it should be for a planet of its size.

When the Moon initially entered orbit, it was a lot closer to Earth than it is today. Throughout the millions of subsequent years, the Moon has gradually moved further away from the Earth and settled into a much longer orbital path. Because of this, eclipses and strong tidal effects were much more common then than they are now.

Observations of Earth s Moon

Based on size and mass, the Moon is the fifth-largest natural satellite in the whole Solar System. By geophysical definition, the Moon is technically a satellite planet. It s significantly larger than every dwarf planet in the Solar System, too that includes Pluto. To put its size into perspective, its diameter is about 25% that of of Earth s, and its surface area is comparable to that of the Americas or Africa.

Its size and proximity to Earth make it clear to see why humans have been observing it for tens of thousands of years at least. The oldest recorded observations of the Moon date back 20-30,000 years ago. Historians believe humans used tally sticks to observe the waxing and waning of the Moon s phases. Ancient Greeks, Babylonians, and even Indian and Chinese astronomers from the 5th and 4th centuries BC made their fair share of observations, as well.

Before the invention of the telescope in the Middle Ages, all observers had to work with their eyes. From the 1600s onward, however, substantial observations of Earth s moon could increase exponentially. With this, Galileo Galilei, Giovanni Battista Riccioli, Francesco Maria Grimaldi, and numerous other astronomers and physicists could pioneer the study of the Moon s geography. Increasingly detailed telescopic observations continued through to the 20th century.

Trips to Earth s Moon

The development of the first legitimate launch systems in the 1950s effectively changed the way we look at the Moon forever. The Space Race kicked off shortly after. Both the Soviet Union and the United States were attempting to send spacecraft into outerspaceduring the early years of the Cold War. While many might think that America led the charge, it was the Soviet Union that accomplished many major milestones first.

The Soviet Union s Luna 1 was the first to exit Earth s gravity and pass near the Moon in 1959. Later that same year, the Luna 2 became the firstspacecraftto reach the surface of the Moon. By the end of 1959, the Luna 3 captured the first photos of the far side of the Moon. By 1966, and 10 came around in 1966, the Soviet Union was the first to accomplish a soft landing (Luna 9) and vehicular orbit (Luna 10).

In 1961, American President John F. Kennedy made a major commitment: the United States would accomplish a crewed mission to the Moon before the end of the 60s. Under the leadership ofNASA, the U.S. launched a series of unmanned probes to the moon. These probes helped NASA scientists and crew better understand the surface of the Moon. As scientists worked tirelessly to learn all there was to know about the surface, the crew trained just as hard to brave the unprecedented elements. They called the programApollo.

The Apollo Program

Between 1961 and 1972, the Apollo program resulted in 32 successful launches, one partial failure, and two total failures. The program cost $25.4 billion in all about $178 billion in today s terms, adjusted for inflation. The first crewed flight, Apollo 7, came in 1968. From that point forward, NASA launched ten more crewed missions to space. The most well-known of these are Apollo 11 and Apollo 13. The former for its success, and the latter for its near-disastrous results.

On July 21st, 1969, Neil Armstrong of Apollo 11 became the first person to walk on the Moon. An estimated half a billion people viewed his walk on television worldwide. On April 11th, 1970, the crew of the Apollo 13 aborted their lunar landing two days into the mission due to a failed oxygen tank in the service module. Instead of continuing toward the Moon, the Apollo 13 crew made the strategic decision to loop around the Moon and slingshot safely back to Earth.

Later Apollo missions entailed the installment of long-lasting observational tools and instruments such as seismometers, magnetometers, and heat flow probes. These instruments transmitted data directly back to Earth until 1977 when the program shuttered due to budget constraints. With this, 1972 s Apollo 17 mission remains the last time a space crew landed on the Moon.

Unmanned Apollo Missions

Spacecraft	Scheduled Date	Launch Summary
AS-201	Feb. 26th, 1966	First Apollo test flight.
AS-203	Jul. 5th, 1966	Second Apollo test flight.
AS-202	Aug. 25th, 1966	Third Apollo test flight.
Apollo 4	Nov. 9th, 1967	First test flight of Saturn V shuttle.
Apollo 5	Jan. 22nd 23rd, 1968	First orbital test flight of the Apollo Lunar Module.
Apollo 6	Apr. 4th, 1968	Second test flight of Saturn V shuttle and Apollo Lunar Module.

Crewed Apollo Missions

Spacecraft	Scheduled Date	Crew Onboard	Launch Summary
AS-204 (Apollo 1)	Feb. 21st, 1967	Gus Grissom Ed White Roger B. Chaffee	Unsuccessful Apollo test flight. All three crew members were killed in a fire on the launch pad.
Apollo 7	Oct. 11th 22nd, 1968	Wally Schirra Walt Cunningham Donn Eisele	Failed Moon landing where the crew famously used the lunar module to return to Earth.
Apollo 8	Dec 21st 27th, 1968	Frank Borman James Lovell William Anders	First crewed test flight of Saturn V and first crewed test flight to the Moon.
Apollo 9	Mar. 3rd 13th, 1969	James McDivitt David Scott Russell Schweickart	Second crewed test flight of Saturn V and first crewed test flight of lunar module and command and service module.
Apollo 10	May 18th 26th, 1969	Thomas Stafford John Young Eugene Cernan	Lunar landing dress rehearsal.
Apollo 11	Jul. 16th 24th, 1969	Neil Armstrong Michael Collins Buzz Aldrin	First crewed Moon landing.
Apollo 12	Nov. 14th 24th, 1969	C. Pete Conrad Richard Gordon Alan Bean	Second crewed Moon landing.
Apollo 13	Apr. 11th 17th, 1970	James Lovell Jack Swigert Fred Haise	Failed Moon landing where crew famously used the lunar module to return to Earth.
Apollo 14	Jan. 31st Feb. 9th, 1971	Alan Shepard Stuart Roosa Edgar Mitchell	Third crewed Moon landing.
Apollo 15	Jul. 26th-Aug. 7th, 1971	David Scott Alfred Worden James Irwin	Fourth crewed Moon landing.
Apollo 16	Apr. 16th 27th, 1972	John Young T. Kenneth Mattingly Charles Duke	Fifth crewed Moon landing.
Apollo 17	Dec. 7th 19th, 1972	Eugene Cernan Ronald Evans Harrison Schmitt	Sixth and final crewed Moon landing of the Apollo program.

How Many Moons Does Earth Have?

While Earth may have just one moon, you can t overstate the Moon s importance throughout human history. It keeps our axis stable, it keeps our tides in tune, and it continues to captivate our imaginations while doing so. While we have been observing and studying it for thousands of centuries, we will undoubtedly continue to do so for just as many years to come. Think of it as a gigantic testament to the power of human exploration and achievement.