At the Edge of Light

This image captures the Moon in a way most of us never see it with the naked eye. Instead of the flat, glowing circle we spot in the night sky, here the surface curves away into shadow, showing off the rough texture of a world covered in craters. The line between light and dark, called the terminator, runs right across the picture. That is where the sun is rising or setting on the lunar surface, and it is exactly there that the craters look sharpest, because the low angle of light casts long shadows across every dent and ridge.

Those craters tell a long story. The Moon has almost no atmosphere and no weather to smooth things over, so the scars left by billions of years of asteroid and meteor impacts just stay put. Some of the big dark patches are called maria, from the Latin word for seas, because early astronomers thought they were actual oceans. They are really vast plains of hardened lava. Images like this one come from NASA spacecraft and telescopes, and they let us study features that are impossible to see clearly from Earth, especially along that shadowed edge where the terrain stands out in the boldest relief.