The so-called ‘transient lunar phenomena’ has been stumping scientists for years – but an explanation may be in the works.

At a mere 240,000 miles away, you’d think we would have figured out everything there is to know about Earth’s little sidekick, the moon. Maybe it’s our short attention span, but it’s almost like: Put men on the moon, check, next stop, Mars.

Case in point: Transient lunar phenomena.

This oddity has been mystifying scientists since at least the 1960s (and likely long before), when a paper by astronomers Barbara Middlehurst and Patrick Moore was published in the journal Science. The scientists has reviewed scientific literature and found nearly 400 reports of strange events on the moon, explains Rafi Letzter on space.com. Calling the unexplained strangeness “lunar transient phenomena” (which got flipped around later), the paper described how regions of the lunar surface would get brighter or darker, and nobody could explain why.

A few years later, the astronomer A. A. Mills wrote in the journal Nature: “The emitted light is usually described as reddish or pinkish, sometimes with a ‘sparkling’ or ‘flowing’ appearance. The coloration may extend for a distance of 10 miles or more on the lunar surface, with brighter spots 2 to 3 miles across, and is commonly associated with veiling of the surface features. The average duration of an event is some 20 minutes, but it may persist intermittently for a few hours.”

Now, some 50 years later, astronomers are finally setting up an observatory specifically to explore the mystery flashing.

While some backyard astronomers can happen upon the flashes, which now occur a few times a week, the new observatory should be well equipped to get some good data. Located in Spain, there will be two cameras constantly trained on the moon. When both register a flash, they will automatically record detailed photos and videos and send them off for analyses.

Who knows what they may discover. Various possibilities have been suggested, including meteor strikes, solar wind hitting moon dust, and the reflection of sunlight – but so far, no explanations have stuck. Except maybe that last one.

“Seismic activities were also observed on the moon. When the surface moves, gases that reflect sunlight could escape from the interior of the moon,” says Hakan Kayal, Professor of Space Technology at Julius-Maximilians-Universität Würzburgand and head of the telescope project. “This would explain the luminous phenomena, some of which last for hours.”

Curiously, interest in this mystery around everyone’s favorite natural satellite has been reignited by a new “race to the moon.” With China, India, and private companies all aiming to visit (and more), it only makes sense that we’d want to figure out what exactly is going on up there.

“Anyone who wants to build a lunar base at some point must of course be familiar with the local conditions,” says Kayal. Pinkish, sparking flashes and all.