The Kepler spacecraft precisely measures the light variations from thousands of distant stars, looking for a moment where the light will change. This light change could signify a planet.
Kepler has a telescope that will focus on the stars that are as large as our Sun. These are the stars that we think may have planets orbiting them. If these stars do have a planet orbiting them then there should be a time where the planet is blocking our solar system’s view of the star. This is known as a transit.
Three or more transits of a given star all with a consistent period, brightness change and duration provide a rigorous method of detection and confirmation. Orbital period can be determined from the time between transits. Orbital size can be determined from the mass of the star and the length of time between transits, and temperature from the planet’s orbit.
The results from this data can be used to calculate the fraction of stars that have planets, as well as the different planetary sizes and orbits for many different types of stars. These results are especially exciting because they will tell us how often planets occur in the habitable zone of other stars.