Earth's Moon

01Overview

The Moon is Earth's only natural satellite and our closest celestial neighbor. It is the brightest object in the night sky after the Sun, and its familiar phases have been observed by humans for millennia. The Moon orbits Earth at an average distance of about 384,400 kilometers (roughly 238,855 miles), but this distance varies slightly because its orbit is not perfectly circular. Its gravitational pull is the main cause of ocean tides on Earth, and it helps stabilize our planet's axial tilt, which in turn stabilizes our climate over long periods.

The Moon is a rocky, airless world about one-quarter the size of Earth. Its surface is covered with craters, mountains, valleys, and large dark plains called maria (Latin for "seas"). These maria are actually vast basins of solidified lava. Because the Moon has no atmosphere, its sky is always black, even during the day, and temperatures swing wildly from about 120°C (250°F) in sunlight to about -130°C (-210°F) in shadow. The Moon does not produce its own light; it shines by reflecting sunlight. As it orbits Earth, we see different portions of its sunlit side, creating the phases we observe from night to night.

The Moon has been a source of wonder and scientific inquiry for centuries. It is the only other world besides Earth that humans have visited, and it remains the only celestial body from which samples have been returned for study. Its proximity and brightness make it an ideal target for beginning stargazers and experienced astronomers alike. Whether you view it with the naked eye, binoculars, or a telescope, the Moon offers a wealth of detail and a connection to our place in the solar system.

02What it is and where to find it

The Moon is a natural satellite, meaning it is a celestial body that orbits a planet—in this case, Earth. It formed roughly 4.5 billion years ago, likely from debris left over after a giant impact between early Earth and a Mars-sized body. The Moon is the fifth largest satellite in the solar system and the largest relative to its parent planet. It is composed primarily of rock and metal, with a small, partially molten core. Its surface is covered in a fine dust called regolith, which is the result of billions of years of meteorite impacts.

Finding the Moon in the sky is straightforward. Because it is so bright, it can often be seen during the day, especially when it is near first quarter or last quarter phase. At night, it is usually the most prominent object in the sky, unless the Sun is up. The Moon rises in the east and sets in the west, much like the Sun, but its rising time changes each day. On average, the Moon rises about 50 minutes later each day, which is why it can be seen at different times of day and night throughout its monthly cycle.

The Moon's position among the stars also changes. It moves along a path called the ecliptic, which is the same path the Sun and planets appear to follow. Because of this, the Moon can sometimes appear close to bright planets like Venus, Jupiter, or Saturn, creating beautiful conjunctions. It can also pass in front of the Sun during a solar eclipse or pass into Earth's shadow during a lunar eclipse. These events are predictable and offer spectacular viewing opportunities. To find the Moon, simply look for the brightest object in the night sky; its position will vary depending on the phase and time of month.

03How to observe it

Observing the Moon requires no special equipment; it is easily visible to the naked eye. However, even a small pair of binoculars or a basic telescope can reveal incredible detail. The best time to observe the Moon is not during a full moon, when the surface appears flat and washed out due to direct sunlight. Instead, look during the partial phases—around first quarter or last quarter—when shadows along the terminator (the line between day and night on the Moon) create strong contrast. This highlights craters, mountain ranges, and other features in stunning relief.

When using binoculars, you can see the larger maria, such as the Sea of Tranquility and the Sea of Serenity, as well as prominent craters like Tycho and Copernicus. A telescope with a modest aperture will reveal finer details: crater walls, central peaks, and rilles (long, narrow depressions). The best views come when the Moon is high in the sky, away from atmospheric turbulence near the horizon. Also, try observing when the Moon is in a dark sky; a bright Moon can wash out faint stars, but that is fine for lunar observing.

For a comfortable experience, use a moon filter to reduce glare, especially with larger telescopes. You can also sketch or photograph the Moon; many stargazers enjoy tracking the changing shadows over several nights. Remember that the Moon is so bright that it can be observed even from light-polluted cities. Its phases repeat roughly every 29.5 days, so you can plan your observing sessions accordingly. Whether you are a beginner or an expert, the Moon offers endless opportunities for exploration.

04History and discovery

The Moon has been observed and studied since prehistoric times. Ancient cultures used the Moon to track time, creating lunar calendars that are still in use in some parts of the world. The Moon's phases were among the first astronomical phenomena to be understood and predicted. Early astronomers, such as the Greek philosopher Anaxagoras, correctly deduced that the Moon shines by reflected sunlight and explained eclipses. Later, in the 17th century, Galileo Galilei turned his telescope to the Moon and discovered its mountains and craters, proving that the Moon was not a perfect, smooth sphere as previously believed.

The modern era of lunar exploration began in the mid-20th century with robotic spacecraft. The Soviet Luna program achieved the first flyby and impact in 1959, and later returned the first images of the far side. The American Apollo program culminated in 1969 with the first human landing on the Moon. Astronauts brought back hundreds of kilograms of lunar rock and soil, which scientists continue to study today. These samples have provided invaluable insights into the Moon's composition, age, and history.

Since the Apollo era, many nations have sent orbiters to map the Moon in detail. These missions have revealed evidence of water ice in permanently shadowed craters near the poles and have helped us understand the Moon's internal structure. The Moon remains a target for future exploration, with plans for new robotic landers and eventually human missions. Its history is intertwined with our own, and studying it helps us understand the early solar system and the processes that shaped our planet.

05Key facts and measurements

The Moon has a diameter of about 3,475 kilometers (roughly 2,159 miles), making it about one-fourth the width of Earth. Its mass is approximately 1.2% of Earth's mass. The average distance from Earth to the Moon is about 384,400 kilometers (238,855 miles), but this varies from about 363,300 kilometers at perigee (closest) to about 405,500 kilometers at apogee (farthest). This variation is why we sometimes see a slightly larger and brighter full moon, often called a supermoon. The Moon's orbit is tilted about 5 degrees relative to Earth's orbit around the Sun, which is why we do not have eclipses every month.

The Moon's surface is marked by thousands of craters, many of which are billions of years old. The largest crater, the South Pole–Aitken basin, is about 2,500 kilometers in diameter and is located on the far side. The Moon's dark maria cover about 16% of its surface, mostly on the near side. The highest point on the Moon is about 10,786 meters above the average surface, while the lowest point is about 9,000 meters below. The Moon has no atmosphere, so its sky is always black, and there is no weather. Its gravity is about one-sixth of Earth's, so you would weigh much less there.

The Moon rotates on its axis in about 27.3 Earth days, which is the same time it takes to orbit Earth. This synchronous rotation means we always see the same face—the near side—from Earth. The far side, often incorrectly called the dark side, receives just as much sunlight as the near side; we simply never see it from Earth. The Moon's phases are caused by its changing position relative to the Sun and Earth, cycling through new moon, first quarter, full moon, and last quarter roughly every 29.5 days. These are just a few of the key measurements that define our closest celestial companion.

06Common misconceptions

One common misconception is that the Moon has a dark side that never sees sunlight. In reality, the far side of the Moon receives just as much sunlight as the near side; it is simply the side we never see from Earth. The term "dark side" is misleading and often confuses people. Another misconception is that the Moon's phases are caused by Earth's shadow. Actually, phases are due to the changing angle between the Sun, Earth, and Moon. Earth's shadow only comes into play during a lunar eclipse, which is a rare event.

Many people believe that the Moon is only visible at night. However, the Moon can often be seen during the day, especially in the morning or afternoon when it is in a crescent or quarter phase. Its brightness makes it stand out against the blue sky. Another myth is that the Moon's gravitational pull affects human behavior or causes strange events. There is no scientific evidence for this; the Moon's gravity primarily affects ocean tides and has negligible effect on humans.

Some think that the Moon is much closer than it really is. The average distance of about 384,400 kilometers is vast; you could fit all the planets in the solar system side by side in that gap. Also, the Moon is not a source of light; it reflects sunlight. Finally, the Moon is not perfectly round; it is slightly flattened and has a bulge toward Earth due to tidal forces. These misconceptions are common, but understanding the facts helps us appreciate the Moon's true nature and our relationship with it.

07Frequently asked questions

Q: Why does the Moon change shape? A: The Moon does not actually change shape; it always remains a sphere. The changing phases are due to its position relative to the Sun and Earth. As the Moon orbits Earth, we see different portions of its sunlit half. When the Moon is between Earth and the Sun, the side facing us is dark, and we call it a new moon. When Earth is between the Sun and the Moon, we see a fully lit face, a full moon. The cycle repeats about every 29.5 days.

Q: Can I see the Moon during the day? A: Yes, the Moon is often visible during the day. It is bright enough to be seen against the blue sky, especially when it is in a crescent or quarter phase. Look for it in the morning or afternoon; its position will vary depending on the phase and time of year. Sometimes it appears near the Sun, but be careful not to look directly at the Sun.

Q: What is a supermoon? A: A supermoon occurs when a full moon coincides with the Moon's closest approach to Earth in its orbit, called perigee. Because it is slightly closer, the Moon appears a bit larger and brighter than an average full moon. However, the difference is subtle and often hard to notice with the naked eye. Supermoons are a popular observing event but are not dramatically different from regular full moons.