NASA’s latest spacecraft, Kepler lifted off into a solar orbit but in a region close to earth.  It’s mission over the next 3 1/2 years is look for Earth-like planets by using a photometer that is very sensitive to variation in the light intensity emitted from stars.  According to Kepler project scientists on a NASA video , the goal of the project is to search the habitable zone, where they think there is water.  In their view, planets that have the right temperature; not too hot, not too cold—like Goldilocks.  

The launch of the Kepler spacecraft, March 6, 2009. It's 3 1/2 year journey will help scientists at NASA answer the question, Is there life out there?

The technology is quite amazing.  The photometer is extremely sensitive to light emitted from a star.  When planets cross the plane of the star, there is a slight flicker in light picked up by Kepler’s photometer.  One scientist put it this way.  Imagine looking at a headlight of car at several hundred feet and being able to detect a flea walking across the headlight.  The camera that I use has about 7 megapixels.  The camera onboard Kepler has more than 96,000 pixels.  So it has extreme sensitivity.  As a planet crosses the plane of a star, as seen in the picture below, the Kepler technology is able to detect the blip in light intensity.  The photograph below shows a drawing of a planet crossing in front of a star as it makes its revolution about the distant star.  Kepler technology is able to detect this motion, and draw conclusions about the size of the planet, and its distance from the star.  

A NASA drawing showing a planet crossing the plane of a star. Kepler technology is able to detect this motion by measuring the light intensity of the star, and looking for "blips."