There’s an astronomical coincidence today: It’s the first full day of summer in the northern hemisphere, and there’s a full Moon. The exact moments of the full Moon and the summer solstice are a bit more than one day apart — a coincidence that happens, on average, once every couple of decades.

At full Moon, it’s daylight across the entire lunar hemisphere that faces our way. But not every location sees the Sun. Some craters near the lunar poles are so deep that sunlight never reaches their bottoms.

That doesn’t mean the crater floors are completely dark. The lighting may be comparable to a family den or even an office building.

Scientists have measured the light levels with a NASA instrument called ShadowCam. It’s on a Korean spacecraft that’s been orbiting the Moon for the past year and a half. The instrument can see into regions that are too dark for other spacecraft.

There’s no atmosphere on the Moon to scatter sunlight. But sunlight that hits the rims of the craters or nearby mountains is reflected into a crater’s depths. Scientists recreated those lighting conditions in an office. And they found that there was plenty of light for working.

Craters near the south pole are prime landing sites for future missions because they may contain a lot of frozen water. Astronauts probably won’t need headlights to find their way around those craters — reflected sunlight should provide all the light they need.

Script by Damond Benningfield