How does Kepler collect starlight to measure transits?
See Animation. The Kepler spacecraft is a single-purpose Schmidt telescope. It stares continuously at a large field of view (see “Where is Kepler pointed?”) to observe more than 100,000 stars simultaneously. The starlight enters the telescope, reflects from the primary mirror to the focal plane array of 42 CCDs. Each 50×25 mm CCD has 2200×1024 pixels (picture elements). The pixels collect the photons of light from the stars. Every 6 seconds, the array “reads out” the number of photons in each pixel to an onboard computer for storage and initial processing. For the selected stars, the data (photon counts) accumulates in an on board computer, and is transmitted to Earth once each month. For more information, see the next question, “How do CDDs (charge coupled devices) work?
