One way to see a dim planet near a bright star is to blot out the star using a device called a coronagraph. This happens to our Sun whenever the Moon moves in front of it during a total solar eclipse. The coronagraph uses a disk to create an artificial eclipse. Since it is one of the few methods that will allow an extra-solar planet to be observed directly, coronagraphs are being developed for use aboard telescopes in space.

Coronagraph - NASA/ESAThe Sun before and after a coronagraph has covered its disk to observe the outer atmosphere, or corona. Nearby stars are millions of times farther away than the Sun, which means they appear millions of times smaller as observed from Earth. Blotting out a star and detecting a nearby planet with a coronagraph presents a tremendous technical challenge.

TPF - NASAScheduled for launch in 2015, the Terrestrial Planet Finder (TPF) will use an advanced coronagraph to view Earth-like planets directly, measuring characteristics that may signal the presence of life. A second TPF mission using different optical techniques may be launched around 2019.

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