How Big Is The Moon?

QUICK ANSWER

The Moon has a diameter of about 2,159 miles (3,476 km), roughly a quarter of Earth's diameter. The Moon is the fifth-largest moon in our solar system and the largest moon relative to its parent planet. About 50 Moons could fit inside Earth by volume, though the Moon's mass is only 1.2% of Earth's.

The Moon is big enough to be a respectable planet in its own right. It's larger than Pluto, smaller than Mercury, and a quarter the size of Earth. Relative to Earth, the Moon is unusually large for a moon, which has played a major role in shaping Earth's history.

How big is the Moon compared to Earth?

About a quarter the size by diameter. According to NASA, the Moon's diameter is 2,159 miles (3,476 km), compared to Earth's 7,918 miles. If you set a single green pea next to a U.S. nickel, you'd have a reasonable representation of the size difference. About 50 Moons could fit inside Earth by volume. The Moon's mass is only about 1.2 percent of Earth's, though, because the Moon is less dense than Earth (no iron core to speak of).

Where does the Moon rank among other moons?

Fifth largest in our solar system. The four bigger moons are Jupiter's Ganymede (the largest, at 3,273 miles diameter), Saturn's Titan, Jupiter's Callisto, and Jupiter's Io. Earth's Moon is just slightly smaller than Io. Several of the moons that rank above ours actually exceed the size of the planet Mercury. The Moon is also unusually large compared to its parent planet: it's about 27 percent of Earth's diameter, while most moons are far smaller percentages of their planets.

Why is the Moon so big relative to Earth?

Because of how it formed. The leading theory is that the Moon formed when a Mars-sized object (sometimes called Theia) collided with the early Earth about 4.5 billion years ago. The collision blasted huge amounts of material into orbit around Earth, which eventually clumped together to form the Moon. Because the Moon formed from existing planetary material rather than being captured or formed independently, it ended up unusually large for a moon. The collision origin also explains why the Moon and Earth have similar isotopic compositions.

Does the Moon's size affect Earth?

Significantly. The Moon stabilizes Earth's axial tilt, which keeps Earth's seasons relatively stable over millions of years. Without the Moon, Earth's tilt could wobble dramatically, causing extreme climate swings. The Moon also drives the tides through its gravity, which has affected coastal ecosystems and weather patterns throughout Earth's history. Some scientists think the Moon's stabilizing influence may have been important for the development of complex life on Earth, though that's harder to prove definitively.

The Moon is about 2,159 miles in diameter, roughly a quarter of Earth's size. It's the fifth-largest moon in our solar system but unusually large relative to its parent planet, due to its violent formation about 4.5 billion years ago. The Moon's size has shaped Earth in ways large and small, from stabilizing our climate to driving the tides that have shaped coastlines for billions of years.

How Big Is The Moon?