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Definition: Astrometry is the area of study that focuses on precise measurements of the positions and movements of stars and other celestial bodies, as well as explaining these movements.

The careful analysis of these celestial motions is crucial in astrophysics and astronomy. The detection of dark matter, for example, was based on finding anomalies between the predictions of how celestial bodies should be moving (based upon the visible matter) and how they were actually moving (based on precise astrometric measurements). Studies of dark energy also require careful astrometry work, in order to correctly determine the distribution and intensity of the repulsive gravity influences.

Applying the methods of astrometry to detect exoplanets was proposed in the 1950s, but did not prove successful until 2009, by Steven Pravdo's team at NASA's Jet Propulsion Laboratory. In this method, the gravitational pull of a planet causes a star to change its orbit over time. Careful analysis of the changes in a star's orbit can provide an indication that there exists a massive exoplanet in orbit around the star. The astrometry technique has benefits over other exoplanet search techniques because it can locate planets that orbit far out from the star (while the other systems tend to detect close-up planets more easily).

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