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.
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