Editing Sirius (section)

=== Kinematics ===
In 1717, [[Edmond Halley]] discovered the [[proper motion]] of the hitherto presumed ''[[fixed stars]]''<ref name="Aitken1942"/> after comparing contemporary [[astrometry|astrometric]] measurements with those from the second century AD given in Ptolemy's ''[[Almagest]]''. The bright stars [[Aldebaran]], [[Arcturus]] and Sirius were noted to have moved significantly; Sirius had progressed about 30 [[arcminutes]] (about the diameter of the Moon) to the southwest.<ref name="Holberg2007-41-42"/>

In 1868, Sirius became the first star to have its velocity measured, the beginning of the study of celestial [[radial velocities]]. Sir [[William Huggins]] examined the [[stellar spectrum|spectrum]] of the star and observed a [[red shift]]. He concluded that Sirius was receding from the Solar System at about 40&nbsp;km/s.<ref name="Daintith1994"/><ref name="Huggins1868"/> Compared to the modern value of −5.5&nbsp;km/s, this was an overestimate and had the wrong sign; the minus sign (−) means that it is approaching the Sun.<ref name="Hearnshaw2014">{{Cite book |last=Hearnshaw |first=John B. |url=https://books.google.com/books?id=HNbSAgAAQBAJ&pg=PA88 |title=The analysis of starlight: two centuries of astronomical spectroscopy |date=2014 |publisher=Cambridge Univ. Pr |isbn=978-1-107-03174-6 |edition=2nd |location=New York, NY |page=88}}</ref>