, a 1980s era study which would have used an interstellar precursor probe to expand the baseline for calculating stellar parallax in support of Astrometry. The history of astrometry is linked to the history of
star catalogues, which gave astronomers reference points for objects in the sky so they could track their movements. 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. 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,
Ptolemy, included a catalogue of 1,022 stars in his work the
Almagest, giving their location, coordinates, and brightness. In the 10th century, the Persian astronomer
Abd al-Rahman al-Sufi carried out observations on the stars and described their positions,
magnitudes and
star color; furthermore, he provided drawings for each constellation, which are depicted in his
Book of Fixed Stars. 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. His observations on
eclipses were still used centuries later in Canadian–American astronomer
Simon Newcomb's investigations on the motion of the Moon, while his other observations of the motions of the planets Jupiter and Saturn inspired French scholar
Laplace's
Obliquity of the Ecliptic and
Inequalities of Jupiter and Saturn. 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. In the 16th century, Danish astronomer
Tycho Brahe used improved instruments, including large
mural instruments, to measure star positions more accurately than previously, with a precision of 15–35
arcsec. Ottoman scholar
Taqi al-Din measured the
right ascension of the stars at the
Constantinople Observatory of Taqi ad-Din using the "observational clock" he invented. Being very difficult to measure, only about 60 stellar parallaxes had been obtained by the end of the 19th century, mostly by use of the
filar micrometer.
Astrographs using astronomical
photographic plates sped the process in the early 20th century. Automated plate-measuring machines and more sophisticated computer technology of the 1960s allowed more efficient compilation of
star catalogues. 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. In the 1980s,
charge-coupled devices (CCDs) replaced photographic plates and reduced optical uncertainties to one milliarcsecond. This technology made astrometry less expensive, opening the field to an amateur audience. 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. During its 4-year run, the positions, parallaxes, and
proper motions of 118,218 stars were determined with an unprecedented degree of accuracy. A new "
Tycho catalog" drew together a database of 1,058,332 stars to within 20-30
mas (milliarcseconds). Additional catalogues were compiled for the 23,882 double and multiple stars and 11,597
variable stars also analyzed during the Hipparcos mission. In 2013, the
Gaia satellite was launched and improved the accuracy of
Hipparcos. The precision was improved by a factor of 100 and enabled the mapping of a billion stars. Today, the catalogue most often used is
USNO-B1.0, an all-sky catalogue that tracks proper motions, positions, magnitudes and other characteristics for over one billion stellar objects. During the past 50 years, 7,435
Schmidt camera plates were used to complete several sky surveys that make the data in USNO-B1.0 accurate to within 0.2 arcsec. ==Applications==