Editing Aldebaran (section)

==Observational history==
[[File:Moon occults Aldebaran.png|thumb|right|upright=1.2|Occultation of Aldebaran by the [[Moon]]. Aldebaran is the red dot to the right, barely visible in the thumbnail.]]
On 11 March AD&nbsp;509, a lunar [[occultation]] of Aldebaran was observed in [[Athens]], [[Greece]].<ref name=lynn/> English astronomer [[Edmund Halley]] studied the timing of this event, and in 1718 concluded that Aldebaran must have changed position since that time, moving several minutes of arc further to the north. This, as well as observations of the changing positions of stars [[Sirius]] and [[Arcturus]], led to the discovery of [[proper motion]]. Based on present day observations, the position of Aldebaran has shifted 7′ in the last 2000 years; roughly a quarter the diameter of the [[full moon]].<ref name=halley/><ref name=burnham/>  Due to [[precession of the equinoxes]], 5,000 years ago the [[Equinox (celestial coordinates)|vernal equinox]] was close to Aldebaran.<ref name=marduk/> Between 420,000 and 210,000 years ago, Aldebaran [[historical brightest stars|was the brightest star]] in the night sky,<ref name=tomkin1998>{{cite journal|last=Tomkin|first=Jocelyn|date=April 1998|title=Once and Future Celestial Kings|journal=Sky and Telescope|volume=95|issue=4|pages=59–63|bibcode=1998S&T....95d..59T}} – based on computations from [[HIPPARCOS]] data. (The calculations exclude stars whose distance or [[proper motion]] is uncertain.) [ftp://tlgleonid.asuscomm.com/HITACHI/BOOK_ASTRO/S&T/SkyandTelescope_1998%20-%20astronomy/04/199804059063.pdf PDF]{{dead link|date=November 2017 |bot=InternetArchiveBot |fix-attempted=yes }}</ref> peaking in brightness 320,000 years ago with an apparent magnitude of {{val|-1.54}}.<ref name=tomkin1998 />

English astronomer [[William Herschel]] discovered a faint companion to Aldebaran in 1782;<ref name=CD/> an 11th-magnitude star at an [[angular separation]] of 117[[arc second|″]]. This star was shown to be itself a close [[double star]] by [[Sherburne Wesley Burnham|S. W. Burnham]] in 1888, and he discovered an additional 14th-magnitude companion at an angular separation of 31″. Follow-on measurements of proper motion showed that Herschel's companion was diverging from Aldebaran, and hence they were not physically connected. However, the companion discovered by Burnham had almost exactly the same proper motion as Aldebaran, suggesting that the two formed a wide [[binary star]] system.<ref name=gore/>

Working at his private observatory in [[Tulse Hill]], [[England]], in 1864 [[William Huggins]] performed the first studies of the spectrum of Aldebaran, where he was able to identify the lines of nine elements, including [[iron]], [[sodium]], [[calcium]], and [[magnesium]]. In 1886, [[Edward Charles Pickering|Edward C. Pickering]] at the [[Harvard College Observatory]] used a photographic plate to capture fifty [[absorption line]]s in the spectrum of Aldebaran. This became part of the [[Henry Draper Catalogue|Draper Catalogue]], published in 1890. By 1887, the photographic technique had improved to the point that it was possible to measure a star's [[radial velocity]] from the amount of [[Doppler shift]] in the spectrum. By this means, the recession velocity of Aldebaran was estimated as {{nowrap|30 miles per second}} (48&nbsp;km/s), using measurements performed at [[Potsdam Observatory]] by [[Hermann Carl Vogel|Hermann C. Vogel]] and his assistant [[Julius Scheiner]].<ref name=clerke/>

Aldebaran was observed using an interferometer attached to the [[Hooker Telescope]] at the [[Mount Wilson Observatory]] in 1921 in order to measure its [[angular diameter]], but it was not resolved in these observations.<ref name=pease/>

The extensive history of observations of Aldebaran led to it being included in the list of 33 stars chosen as benchmarks for the [[Gaia mission]] to calibrate derived stellar parameters.<ref name=sahldoldt/>  It had previously been used to calibrate instruments on board the [[Hubble Space Telescope]].<ref name=heiter/>