That's No Moon!

That's a minimoon, actually. And while there's one big Moon that everyone knows and loves, it's not the only natural satellite that orbits the Earth:

Scientists believe that at any given time there are about a thousand larger-than-a-softball minimoons in our planet's gravitational pull, and about one or two of those are the size of dishwashers. They stay around Earth for between six and 18 months before heading off, back in thrall to the sun's gravitational pull.
Larger minimoons arrive too, but less frequently. A minimoon about the size of a school bus probably comes and hangs out every half century or so; one the size of a football field may come about once every 100,000 years. "A hundred thousand years is about the time frame that human beings have been doing things like leaving their handprints on cave walls, so maybe in that time frame somebody once actually looked into the sky and saw a mini-moon moving across the sky," Robert Jedicke, who studies these minimoons, told National Geographic last year.

More from The Atlantic.