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.
The X is visible only for a few hours before the first quarter. To find the X look along the lunar terminator, the line between dark and light, start at about the middle and follow it slightly south. Near to the X, the Lunar V is also visible, formed by Ukert crater and several other small craters.
Lunar X visibility in 2014
Jan 8 2014 16:12 UT
Feb7 2014 06:46 UT
Mar 8 2014 20:19 UT
Apr 7 2014 08:38 UT
May 6 2014 19:56 UT
Jun 5 2014 06:36 UT
Jul 4 2014 17:11 UT
Aug 3 2014 04:11 UT
Sep 1 2014 15:59 UT
Oct 1 2014 04:51 UT
Oct 30 2014 18:45 UT
Nov 29 2014 09:25 UT
Dec 29 2014 00:21 UT