March 11, 2009
The Moon has changed phase thousands of times since the beginning of the cosmos, but only once did it shine on the night you arrived.
Lunar X
Birthday · March 11, 2009
A little universe, just for you
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APOD published March 11, 2009. Credit: Catching the Light. A publication-date match, not a photo taken on your date. Independent of NASA.
The striking X near the center of this lunarscape is easily visible in binoculars or a small telescope. Yet, not too many have seen it. The catch is, this lunar X is only apparent during a four hour period just before the Moon's first quarter phase. At the terminator, or shadow line between lunar day and night, the X illusion is produced by a configuration of the craters Blanchinus, La Caille and Purbach. Near the Moon's first quarter phase, an astronaut standing close to the craters' position would see the slowly rising Sun very near the horizon. Temporarily, the crater walls would be in sunlight while the crater floors were still in darkness. Seen from planet Earth, contrasting sections of bright walls against the dark floors by chance look remarkably like an X. This sharp image of the Lunar X was captured at approximately 11:59 UT on March 3, 2009. The Moon's first quarter phase was at 7:46 UT on March 4.
Image credit: Catching the Light