Exploring Outer Worlds
Since the early 1990s, astronomers have known that distant planets orbit stars light-years from Earth. Although most of these alien worlds, called exoplanets, are too far away to be imaged directly, scientists have made detailed observations of their size and composition. One method of study involves watching a planet as it transits its host star. By measuring how the brightness and color of a star changes when a planet crosses in front of its disk, astronomers can indirectly determine the mass of the planet and the proximity of its orbit. Similar measurements can provide other key information, like the chemical makeup of a planet's atmosphere. Watch the video to learn more.
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NASA's Goddard Space Flight Center
Cover image courtesy of ESA/Hubble