A rare clair-obscur effect occurring when the Moon is at first quarter, a bright X appears on the surface of the moon along the divide between light and darkness near the Moon’s south pole. An equally bright V appears at the same time near the Moon’ north pole.

Viewing this phenomenon usually requires binoculars or a telescope. Look for the half-lit Moon in the southwestern sky around sunset and focus on the divide between darkness and light, called the terminator. The X is formed by sunlight illuminating the rims of the Blanchinus, La Caille and Purbach craters. Likewise, the V is created by sunlight on the Ukert crater and several other small craters.

Photo by Kym MacKinnon on unsplash