The thread Alex started about chromatic aberration in the eyeball reminded me of an odd visual effect I've noticed two or three times. I recall first seeing it when observing Comet Hale-Bopp.
As I was looking for detail in and around the coma, the entire comet was suddenly covered by what looked like a faint, highly detailed and irregular moire pattern. It was more obvious where it was superimposed on the comet, but extended somewhat beyond. Although I knew it was not really there, I couldn't convince my eye/brain it wasn't. I never saw it again on later nights when observing Hale-Bopp, but it happened once when I was looking at M13, and I believe one other time. Very odd.
Clear skies, Alan
As I was looking for detail in and around the coma, the entire comet was suddenly covered by what looked like a faint, highly detailed and irregular moire pattern. It was more obvious where it was superimposed on the comet, but extended somewhat beyond. Although I knew it was not really there, I couldn't convince my eye/brain it wasn't. I never saw it again on later nights when observing Hale-Bopp, but it happened once when I was looking at M13, and I believe one other time. Very odd.
Clear skies, Alan
