Earth’s moon is a prominent feature in our night sky, but how does its size stack up against other moons in our solar system? While it’s significantly smaller than Earth, it’s surprisingly large compared to many other moons orbiting other planets. Let’s explore the moon’s dimensions and its ranking among its celestial counterparts.
The moon is a little more than one-quarter the size of Earth. (Image credit: CochiseVista via Getty Images)
Measuring the Moon: Dimensions and Comparisons
The moon boasts a mean radius of 1,079.6 miles (1,737.5 kilometers), resulting in a mean diameter of 2,159.2 miles (3,475 km). This makes it less than a third the width of Earth. To put it in perspective, if Earth were the size of a nickel, the moon would be about as big as a coffee bean.
Its equatorial circumference stretches 6,783.5 miles (10,917 km). While the moon may appear large in our sky due to its proximity to Earth (an average distance of 238,855 miles or 384,400 km), its surface area is only about 14.6 million square miles (38 million square km). This is smaller than the total surface area of Asia.
The Moon’s Size Relative to Earth: A Unique Ratio
The moon is roughly 27% the size of Earth, a significantly larger ratio (1:4) than any other planet-moon pairings in our solar system. This substantial size difference makes the Earth-Moon system quite unique.
Lunar Mass, Density, and Gravity
Although large compared to other moons, the moon’s mass is only about 1.2% of Earth’s mass, meaning Earth weighs 81 times more than the moon. The moon’s density is 3.34 grams per cubic centimeter (3.34 g/cm3), about 60% of Earth’s density. Interestingly, this makes it the second densest moon in the solar system, second only to Jupiter’s moon Io.
The moon’s gravitational pull is about 16.6% of Earth’s gravity. This means a person weighing 100 lbs on Earth would weigh only about 16.6 lbs on the moon.
The Deep Space Climate Observatory captured this image of the Earth and Moon. (Image Credit: NASA/NOAA)
Comparing the Moon to Other Moons in the Solar System
While the moon is large compared to Earth, it ranks fifth in size among all moons in our solar system. Ganymede, a moon of Jupiter, holds the title of the largest moon, with Titan, Callisto, and Io (all Jovian moons) taking the second, third, and fourth spots, respectively.
| Rank | Moon | Equatorial Radius (miles) | Parent Planet |
|---|---|---|---|
| 1 | Ganymede | 1,635 | Jupiter |
| 2 | Titan | 1,600 | Saturn |
| 3 | Callisto | 1,497 | Jupiter |
| 4 | Io | 1,131.7 | Jupiter |
| 5 | Earth’s Moon | 1,079.6 | Earth |
Conclusion: A Uniquely Large Moon
While not the largest moon in the solar system, Earth’s moon is exceptionally large compared to its host planet. This unique characteristic distinguishes the Earth-Moon system from others and contributes to the fascinating lunar phenomena we observe, such as supermoons and the moon illusion. The moon’s size relative to Earth plays a crucial role in its gravitational influence on our planet, affecting tides and other natural processes. Its relatively large size also makes it a prominent and captivating object in our night sky.
