A Virgin Atlantic passenger plane flies in the sky with the moon seen in the background, in London, Britain January 19, 2016. (Photo by Toby Melville/Reuters)
The supermoon rises behind Glastonbury Tor on September 27, 2015 in Glastonbury, England. Tonight's supermoon, so called because it is the closet full moon to the Earth this year, is particularly rare as it coincides with a lunar eclipse, a combination that has not happened since 1982 and won't happen again until 2033. (Photo by Matt Cardy/Getty Images)
A partial Solar eclipse is seen just after sunrise over the Queens borough of New York across the East River on November 3, 2013 in New York. (Photo by Stan Honda/AFP Photo)
A hot air balloon floats past an almost full rising moon on a warm fall evening near Encinitas, California October 5, 2014. (Photo by Mike Blake/Reuters)
The moon rises behind Reunion Tower in downtown Dallas, Sunday evening, November 13, 2016. On Monday the supermoon will be the closest full moon to earth since 1948, and it won't be as close again until 2034. (Photo by Tom Fox/The Dallas Morning News via AP Photo)
A “super blood blue moon” is seen during an eclipse behind an elephant statue at a temple in Bangkok, Thailand, January 31, 2018. (Photo by Athit Perawongmetha/Reuters)
An incredible moon rise behind the World Trade Center, Manhattan, New York on August 23, 2016. The breath-taking photo was taken by photographer Jennifer Khordi. She said: it was just absolutely amazing to see this. (Photo by Jennifer Khordi/Caters News Agency)
Our moon is a pretty big object. It's big enough to be a respectable planet in its own right, if it were orbiting the sun instead of the Earth. (Actually, it is orbiting the sun in a nearly perfectly circular orbit, that the Earth only slightly perturbs... but that's a topic for another day.) The Moon is a quarter the diameter of the Earth. Only Pluto has a satellite that is larger, in proportion to the size of the planet it orbits.