Search for Planets
This method measures the decrease in the brightness of a star when a planet passes in front of it. For a Jupiter-sized planet the dimming represents about 1% of the starlight. This method is most effective for large planets orbiting very close to the star. The first planetary transit to be observed by a ground-based telescope was for the planet orbiting the star named HD 209458.
Click on the thumbnail below to learn about how the photometry data that proved that the star named HD 209458 had its own planet:
Europe's COROT planet-hunting space telescope is already at work. From its polar orbit, it is looking for rocky planets several times larger than Earth around nearby stars.