Lunar X

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

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
  1. ^ Rice, Tony. "X marks the moon on Thursday night". WRAL.
  2. ^ a b Harrington, Philip S. (2010). Cosmic challenge : the ultimate observing list for amateurs. Cambridge: Cambridge University Press. p. 1999. ISBN 978-0-521-89936-9.
  3. ^ Chapman, David M.F. "The Lunar X Files: a fleeting vision near the crater Werner" (PDF). Willingboro Astronomical Society.