Astrometry

This can be dated back to the ancient Greek astronomer Hipparchus, who around 190 BC used the catalogue of his predecessors Timocharis and Aristillus to discover Earth's precession.

[2] Hipparchus's successor, Ptolemy, included a catalogue of 1,022 stars in his work the Almagest, giving their location, coordinates, and brightness.

Egyptian mathematician Ibn Yunus observed more than 10,000 entries for the Sun's position for many years using a large astrolabe with a diameter of nearly 1.4 metres.

Like the earlier catalogs of Hipparchus and Ptolemy, Ulugh Beg's catalogue is estimated to have been precise to within approximately 20 minutes of arc.

In 1872, British astronomer William Huggins used spectroscopy to measure the radial velocity of several prominent stars, including Sirius.

Started in the late 19th century, the project Carte du Ciel to improve star mapping could not be finished but made photography a common technique for astrometry.

[citation needed] In 1989, the European Space Agency's Hipparcos satellite took astrometry into orbit, where it could be less affected by mechanical forces of the Earth and optical distortions from its atmosphere.

Operated from 1989 to 1993, Hipparcos measured large and small angles on the sky with much greater precision than any previous optical telescopes.

[15] NASA's planned Space Interferometry Mission (SIM PlanetQuest) (now cancelled) was to utilize astrometric techniques to detect terrestrial planets orbiting 200 or so of the nearest solar-type stars.

By studying these images, they can detect Solar System objects by their movements relative to the background stars, which remain fixed.

Quaoar and Sedna are two trans-Neptunian dwarf planets discovered in this way by Michael E. Brown and others at Caltech using the Palomar Observatory's Samuel Oschin telescope of 48 inches (1.2 m) and the Palomar-Quest large-area CCD camera.

The ability of astronomers to track the positions and movements of such celestial bodies is crucial to the understanding of the Solar System and its interrelated past, present, and future with others in the Universe.

Illustration of the use of interferometry in the optical wavelength range to determine precise positions of stars. Courtesy NASA/JPL-Caltech
Concept art for the TAU spacecraft , a 1980s era study which would have used an interstellar precursor probe to expand the baseline for calculating stellar parallax in support of Astrometry.
Diagram showing how a smaller object (such as an extrasolar planet ) orbiting a larger object (such as a star ) could produce changes in position and velocity of the latter as they orbit their common center of mass (red cross).
Motion of barycenter of solar system relative to the Sun