When Titan passed in front of the X-ray bright Crab Nebula on January 5, 2003, it gave astronomers a rare opportunity to study its X-ray shadow (inset). Chandra’s precise measurement of Titan’s shadow enabled astronomers to determine that its X-ray absorbing atmosphere has a height of about 550 miles (880 kilometers). This may have been the first transit of the Crab Nebula by Titan since the nebula was formed by a supernova that was observed to occur in the year 1054. The next similar conjunction will take place in the year 2267.