Recently, while reading some forum posts on the website, Our Dark Skies, I learned of an upcoming opportunity to view an optical feature on the moon called the Lunar “X”. During a narrow window around 1st. quarter moon, sunlight illuminates some of the crater ridges near the craters Werner, Purbach, Blanchinus & La Caille, forming the letter “X”. I’ve never seen or heard of this feature and I was curious to see if I could view it. Using an 80 mm f/11 refractor with a 24mm eyepiece (about 38x), I was able to spot the white “X” about 1/3 of the way up from the bottom of the moon along the terminator. It was small but obvious. I made a sketch of the view.

The Lunar “X”
For more information on the Lunar “X”, check Wikipedia: http://the-moon.wikispaces.com/Lunar+X
Ann T.
UPDATE
Here is a picture of the Lunar X that I took tonight, after Ann brought it to our attention, and you can see how closely it matches Ann’s drawing. Thanks Ann, it was really worth seeing.
John G.

The Lunar X
Great photo, John! I’m so glad you were able to photograph it. The “X” is only visible for about 4 hours at 1st. quarter. Its appearance began at about 2230 UT (5:30 EST) last night, so you caught it just before it disappeared.
Ann T.