X and V on the Moon'

At certain times, the moon shows features which have been given names according to their shape.

The Lunar X is a clair-obscur or chiaroscuro effect in which light and shadow creates the appearance of a letter 'X' on the rim of the Blanchinus, La Caille and Purbach craters.

The X is visible only for a few hours before the first quarter, slightly below the lunar terminator. Above the X, the Lunar V is also visible, formed by Ukert crater and several other small craters.

Here's a labelled version: