Emily Starbug Photography
The Purbach Cross
Taken with a Skywatcher 130p and a Philips webcam. 370 frames at 5 f/s. Processed in Registax 6. Seeing was not good for this image as it was very boily and unsteady.
This is a famous "optical feature" on the Moon, which appears like the letter "X" when the terminator is at a suitable position. It is a fine example of how the combination of lighting and topography can combine to produce a pattern that repeats on each lunation, but only for a short time. The illusion of the "X" is created by sunlight falling on the rims/ridges between the craters La Caille, Blanchinus, and Purbach.
The "X" is observable for about 4 hours around the lunar First Quarter.
The Purbach Cross
Taken with a Skywatcher 130p and a Philips webcam. 370 frames at 5 f/s. Processed in Registax 6. Seeing was not good for this image as it was very boily and unsteady.
This is a famous "optical feature" on the Moon, which appears like the letter "X" when the terminator is at a suitable position. It is a fine example of how the combination of lighting and topography can combine to produce a pattern that repeats on each lunation, but only for a short time. The illusion of the "X" is created by sunlight falling on the rims/ridges between the craters La Caille, Blanchinus, and Purbach.
The "X" is observable for about 4 hours around the lunar First Quarter.