Tracking SDO's Attitude With the Stars
How does SDO know where it is pointing? Seems easy, just point at the brightest object in the sky! But what about our roll angle around the Sun, or where is the Sun's North Pole? SDO uses star trackers to measure its attitude. CCD images are compared to a library to see where the star tracker is pointed. Once we know where the star trackers point we can figure out our roll angle on the Sun.