How Many Moons Does Earth Have?

Key Points

• Earth’s moon is believed to have originated from a collision between Earth and an ancient planet called Theia, forming 4.5 billion years ago.
• The Moon is the fifth-largest natural satellite in the Solar System and is larger than every dwarf planet, including Pluto.
• The Soviet Union achieved major milestones in lunar exploration, including the first spacecraft to reach the Moon’s surface and capture photos of the far side of the Moon.
• The Apollo program resulted in 32 successful launches, including the iconic Apollo 11 mission where Neil Armstrong became the first person to walk on the Moon.

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 the 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

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 the 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 back 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 as well, and 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 outer space during 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 first spacecraft to 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 of NASA, 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 program Apollo.

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 into 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 shut down 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

Crewed Apollo Missions

How Many Moons Does Earth Have?

While the 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.

The image featured at the top of this post is ©Elena11/Shutterstock.com.