Sightings of these rare, shimmering clouds on the edge of space are on the rise. No one knows why.

It’s a wild time of year to look at clouds in Oklahoma, and Keith Cook can attest to that. But the clouds he spotted over the weekend from near Enid weren’t associated with any supercell thunderstorms. Instead, they were clouds at the edge of space.

Cook stumbled upon the rare noctilucent cloud. They form 50 miles up, in a region of the atmosphere called the mesosphere. All of our weather-producing clouds live far lower — generally less than 50,000 feet — in the troposphere.