Kepler: The search for habitable planets

Kepler will detect alien worlds by measuring the minuscule dimming of a star's light that occurs when a planet passes in front of it Photograph: Ames Wendy Stenzel/Nasa

The Milky Way, showing our sun about 25,000 light years from the galaxy's centre. The yellow cone illustrates the region or 'starfield' in which Kepler will hunt for habitable planets Photograph: Jon Lomberg/Nasa

When a planet passes in front of its sun this causes a mind-bogglingly tiny change in the star's overall brightness. “If Kepler were to look down at a small town on Earth at night from space, it would be able to detect the dimming of a porch light as somebody passed in front,” says James Fanson, project manager at Nasa’s Jet Propulsion Laboratory in California. An orbiting planet will produce a regular, periodic change in the brightness of its star Photograph: Nasa

The exterior of the complete spacecraft (left) and a cutaway of the photometer with the major components labelled Photograph: Nasa

Installing the solar array assembly Photograph: Ball Aerospace/Nasa

The fully assembled Kepler spacecraft and photometer Photograph: Ball Aerospace/Nasa

If the entire Kepler craft is an eye, the 'focal plane array' is its retina. It consists of 42 charge coupled devices (CCDs), each 2.8 by 3.0cm with 1,024 by 1,100 pixels, adding up to 95 megapixels for the whole array Photograph: Ball Aerospace/Nasa

The focal plane assembly showing the array of 42 CCDs in place Photograph: Ball Aerospace/NASA

Kepler's primary mirror, which acts like a lens focusing light onto the detectors Photograph: Ball Aerospace/Nasa

Technicians inspect the primary mirror's coating Photograph: Ball Aerospace/Nasa

Rear view revealing the primary mirror's weight-saving honeycomb structure. The mirror only weighs a seventh the weight of a solid mirror of the same size Photograph: Ball Aerospace/Nasa

Technicians work on the Schmidt corrector plate, which corrects optical distortions known as spherical aberration Photograph: Ball Aerospace/NASA

The spacecraft is guided onto the third stage of a Delta II rocket Photograph: Troy Cryder/NASA

On Launch Pad 17-B at Cape Canaveral Air Force Station in Florida, the first half of the fairing is moved into place around Kepler atop its Delta II rocket. The fairing fits flush with the outside of the rocket and forms an aerodynamically smooth nose cone that protects the spacecraft during launch and ascent Photograph: Nasa