March 13, 2007Y
ou might have seen the lunar eclipse March 3, when Earth's shadow covered the Moon and turned it red. But NASA's STEREO-B satellite saw something even more spectacular February 25: the movement of the Moon across the Sun's disc. In other terms, a lunar transit of the Sun.
NASA engineers had deliberately arranged for the observation in order to calibrate their camera against the black disc of the backlit Moon. This allows them to measure and later remove "dark current" leaking from the camera's CCD light detectors, improving image quality.
STEREO-A and STEREO-B are a pair of satellites observing the Sun from different points of view. The data are used to create stereo images and animations of solar storms.Click here
to view a movie of the transit.