Since 1995, more than 500 planets have been discovered to be orbiting stars outside our solar system. These exoplanets—terrestrial and larger planets orbiting other stars—are detected with help from NASA's Kepler spacecraft, which launched in March 2009 with the goal of using the transit technique to detect exoplanets. With this method, planets that pass in front of their host stars block out some of the starlight causing the star to dim slightly for a few hours. The Kepler spacecraft stares at a field of stars in the Cygnus constellation and records the brightness of those stars every thirty minutes to search for transiting planets.

The time series of brightness measurements for a star is called a light curve. The Kepler spacecraft beams data for more than 150,000 stars to Earth at regular intervals. With every download of data, the time baseline of the light curves is extended. The Kepler team's computers are sifting through the data, but the Planet Hunters project is betting that there will be planets that can only be found via the human ability for pattern recognition.

NASA is releasing light curves into the public archive to encourage broader participation, which is where you come in. Planet Hunters is an online experiment that taps into the power of human pattern recognition. Participants are partners with Zooniverse's science team, who will analyze group assessments, obtain follow up observations at the telescope to understand the new classification schemes for different families of light curves, identify oddities, and verify transit signals. The main interface plots Kepler's data on a chart and asks the citizen scientist questions about what they see, such as patterns or dips in light.