* Astronomy

The Werner X is a famous optical phenomena on the Moon, which appears like an chiaroscuro 'X' shape, when the lunar sunrise falls on the rims and ridges between the craters La Caille, Purbach, and Blanchinus.
The Werner X (Also called Lunar X and the Purbach Cross) is visible each month for approximately 4 hours during the lunar First Quarter.

Sunrise on the Moon - the Werner X

The Purbach Cross