Purbach's Cross / Lunar X on June 15, 2013

I've tried before to get a good shot of the Lunar X or Purbach's Cross. I noticed that I accidentally got the X in an earlier shot before I knew how to stack images to reduce noise, so I wanted to make a more deliberate attempt.

The X is clearly visible about 3/4 down the terminator of the lunar disc. Although the "Lunar terminator" sounds like a great science fiction movie, it's basically "the division between the illuminated and dark parts of the Earth's Moon. It is the lunar equivalent of the division between night and day" (Wikipedia).

I usually try to see the X around Half Moon (50%) but it actually occurs much sooner. Using a lunar phase iPhone app, this X occurred at 43.25% illumination.

Sorry for the JPG, Blogger was being funky and said my PNG wasn't an image file for some reason.