A Planet's telltale signature

This diagram illustrates how a planet passing in front of a star blocks a tiny amount of starlight. In this case, it's a planet crossing the face of a nearby star called HD 209458, located 153 light-years from Earth in the constellation Pegasus. The dip in the center of the diagram represents a 1.7 percent drop in starlight over a three-hour period as the planet moves across the star's disk. By watching this eclipse, astronomers can confirm a planet's existence.