What is a transiting planet?
A transiting planet is one whose orbit takes it in front of (and also generally behind) its star once per orbit as seen from Earth. This geometry makes it much easier to measure those planets. From the transit (planet passing in front of star) we can measure the radius of the planet. From the eclipse (planet passing behind star) we can measure the amount of energy radiated by the planet in the infrared. Together these numbers (radius and emitted energy) give us a planetary temperature. Until now, only transiting planets have been directly measured.
