SALLY BENSUSEN / SCIENCE PHOTO LIBRARY SALLY BENSUSEN / SCIENCE PHOTO LIBRARY
Stellar wobble. Artwork of a star and an orbiting planet showing the reasons for stellar (star) wobble. Stellar wobble is an effect observable from Earth which implies the presence of an orbiting planet. Here, the star is yellow, and the planet red. The bodies orbit around a common centre of gravity (green line). At top and bottom, the star is moving towards the observer, and in the third frame down, it is moving away. This motion affects the wavelength of the light as seen from Earth, allowing the orbital velocity and the mass of the planet to be inferred. Several stars have been shown to have planets by this method, including 51 Pegasi and 47 Ursae Majoris.
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