Lunar X

For the Google-sponsored competition, see Google Lunar X Prize.

The Lunar X (also known as the Werner X) is a clair-obscur effect in which light and shadow creates the appearance of a letter 'X' on the rim of the Blanchinus, La Caille and Purbach craters of the Moon.^[1]

Lunar X formation taken January 30, 2012, the formation is off the center towards the right

Lunar X and Lunar V recorded on a Skywatcher 150/750 with a ASI294MC Pro on May 29, 2020, in Mainz, Germany

The X is visible only for a few hours before the first quarter,^[2][3] slightly below the lunar terminator. Near to the X, the Lunar V is also visible, formed by Ukert crater and several other small craters.^[2]

Half waxing moon with inset closeup of Lunar X, used by a 60mm refractor telescope