Lunar X
The Lunar x (also known as the Werner x or Purbach Cross) is a clair-obscur effect created on the moon by light and shadow on the rim of the Blanchinus, La Caille and Purbach craters that appears in the form of the letter X.
The X is visible only for a few hours before the first quarter.[1][2]
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.
Nearby the x the Lunar v is also visible, formed by Ukert crater and several other small craters[1]
References
- ^ a b Harrington, Philip S. (2010). Cosmic challenge : the ultimate observing list for amateurs. Cambridge: Cambridge University Press. p. 1999. ISBN 0-521-89936-2.
- ^ Chapman, David M.F. "The Lunar X Files: a fleeting vision near the crater Werner" (PDF). Willingboro Astronomical Society.