How far away is the moon?

It may seem like a question with a simple answer: How far away is the moon? But the distance between Earth and our closest neighbor is more nuanced than a single number.

"The commonly quoted average distance of 384,400 kilometers, or 238,855 miles, is a good approximation," said Craig Hardgrove, an associate professor of Earth and space exploration at Arizona State University and principal investigator on LunaH-Map, a remote mission designed to detect ice deposits on the moon.

However, the moon's orbit around the Earth is elliptical, so its distance from Earth varies," Hardgrove told Live Science in an email.

That distance ranges from roughly 221,500 miles (356,470 km) away at its closest point to Earth, called perigee, to 252,000 miles (405,600 km) away at its farthest point, called apogee, Hardgrove said.

The distance at apogee is so great, the solar system's seven other planets (Mercury, Venus, Mars, Jupiter, Saturn, Uranus and Neptune) could fit between Earth and the moon, astronomer Phil Plait wrote for Slate. This thought experiment works if the average diameters of the planets are added together, which equals 236,100 miles (380,016 km).

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We can thank the Apollo astronauts for the accuracy of these measurements, Hardgrove said. Using reflectors left on the lunar surface in the 1960s and '70s, scientists today can shine high-powered lasers at the moon and measure their reflection speed to determine the satellite's distance from Earth.