Un X au premier quartier de Lune - First Quarter Moon and The Lunar X...

Un X au premier quartier de Lune - First Quarter Moon and The Lunar X - La Lune seen on March 3, 2009, about twenty hours before the first quarter. Down the image, close to the terminator, a white “” x” is visible. Easily observable in binoculars, this formation is visible only a few hours a month, shortly before the first moonquarter. This particular formation appears when the Sun illuminates the walls of Blanchinus, La Caille and Purbach crateres. The Lunar “” X”” is an interesting formation created by the walls of craters Blanchinus, La Caille and Purbach that appears in the form of the letter X when illuminated by the Sun for a brief period of time around first quarter. The formation is also known as the Purbach Cross and the Werner X. The optical illusion is relatively unknown because it is visible for only about 4 hours just before first quarter. The X stands out when just the rims of the craters are illuminated and the floors are in the deep shadows of lunar night along the terminator. When the Sun shines into the craters, the X blends into its surroundings, looking like the normal cratered lunar landscape. These photos were taken at approximately 6:59 p.m. est (11:59 UT) on March 3, 2009. First quarter occurred at 2:46 a.m. east (7:46 UT) on March 4