NASA Camera Calibration Catches Moon in Transit|
Mike Pasini, The Imaging Resource
(Tuesday, March 13, 2007 - 12:05 EDT)
Scientists calibrate some cameras aboard the STEREO-B spacecraft and see the moon pass over a grapefruit sun.
Capturing four wavelengths of extreme ultraviolet light, NASA scientists happened to record the sun just as the moon passed between the STEREO-B spacecraft and the sun.
They were calibrating the dark current of STEREO-B's CCD detectors, pointing to something black to see what pixels were still (and falsely) bright. The hyperactive pixels are subsequently subtracted from other images to get a more accurate portrait of celestrial celebrities.
You can read the full account here, which contains links to the movie of the moon passing before the sun, too.