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'''Astrometry''' is the branch of [[astronomy]] that relates to precise [[measurements]] and explanations of the positions and movements of [[stars]] and other [[celestial]] bodies. Although once [[thought]] of as an [[esoteric]] field with little useful [[application]] for the [[future]], the [[information]] obtained by astrometric measurements is now very important in contemporary [[research]] into the kinematics and [[physical]] [[origin]] of our [[Solar System]] and our [[Galaxy]], the [[Milky Way]].

'''Astrometry''' is the branch of [[astronomy]] that relates to precise [[measurements]] and explanations of the positions and movements of [[stars]] and other [[celestial]] bodies. Although once [[thought]] of as an [[esoteric]] field with little useful [[application]] for the [[future]], the [[information]] obtained by astrometric measurements is now very important in contemporary [[research]] into the kinematics and [[physical]] [[origin]] of our [[Solar System]] and our [[Galaxy]], the [[Milky Way]].

==History==

==History==

The [[history]] of '''astrometry''' is linked to the history of [http://en.wikipedia.org/wiki/Star_catalogue star catalogues], which gave [[astronomers]] [[reference]] points for objects in the sky so they could track their [[Motion|movements]]. This can be dated back to [http://en.wikipedia.org/wiki/Hipparchus Hipparchus], who around 190 BC used the catalogue of his predecessors [http://en.wikipedia.org/wiki/Timocharis Timocharis] and [http://en.wikipedia.org/wiki/Aristillus Aristillus] to [[discover]] the [[earth]]’s [http://en.wikipedia.org/wiki/Precession precession]. In doing so, he also developed the brightness scale still in use today. Hipparchus compiled a catalogue with at least 850 stars and their positions. Hipparchus's successor, [http://en.wikipedia.org/wiki/Ptolemy Ptolemy], included a catalogue of 1,022 stars in his work the [http://en.wikipedia.org/wiki/Almagest Almagest], giving their location, coordinates, and brightness.

The [[history]] of '''astrometry''' is linked to the history of [https://en.wikipedia.org/wiki/Star_catalogue star catalogues], which gave [[astronomers]] [[reference]] points for objects in the sky so they could track their [[Motion|movements]]. This can be dated back to [https://en.wikipedia.org/wiki/Hipparchus Hipparchus], who around 190 BC used the catalogue of his predecessors [https://en.wikipedia.org/wiki/Timocharis Timocharis] and [https://en.wikipedia.org/wiki/Aristillus Aristillus] to [[discover]] the [[earth]]’s [https://en.wikipedia.org/wiki/Precession precession]. In doing so, he also developed the brightness scale still in use today. Hipparchus compiled a catalogue with at least 850 stars and their positions. Hipparchus's successor, [https://en.wikipedia.org/wiki/Ptolemy Ptolemy], included a catalogue of 1,022 stars in his work the [https://en.wikipedia.org/wiki/Almagest Almagest], giving their location, coordinates, and brightness.

In the 10th century, Abd al-Rahman al-Sufi carried out observations on the stars and described their positions, magnitudes, brightness, and colour, and gave drawings for each constellation, in his Book of Fixed Stars. 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. His observations on eclipses were still used centuries later in Simon Newcomb's investigations on the motion of the moon, while his other observations inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn's.[clarification needed][4] In the 15th century, the Timurid astronomer Ulugh Beg compiled the Zij-i-Sultani, in which he catalogued 1,019 stars. 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.[5]

In the 10th century, Abd al-Rahman al-Sufi carried out observations on the stars and described their positions, magnitudes, brightness, and colour, and gave drawings for each constellation, in his Book of Fixed Stars. 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. His observations on eclipses were still used centuries later in Simon Newcomb's investigations on the motion of the moon, while his other observations inspired Laplace's Obliquity of the Ecliptic and Inequalities of Jupiter and Saturn's.[clarification needed][4] In the 15th century, the Timurid astronomer Ulugh Beg compiled the Zij-i-Sultani, in which he catalogued 1,019 stars. 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.[5]