Editing Stellar parallax (section)

{{Short description|Changed position of star vs background}}
{{Use dmy dates|date=January 2019}}
{{broader|Parallax in astronomy}}
[[File:Stellarparallax parsec1.svg|thumb|right|Stellar parallax is the basis for the [[parsec]], which is the distance from the [[Sun]] to an [[astronomical object]] that has a [[parallax]] angle of one [[arcsecond]]. (1 [[astronomical unit|AU]] and 1 parsec are not to scale, 1 parsec = ~206265 AU)]]

'''Stellar parallax''' is the apparent shift of position (''[[parallax]]'') of any nearby star (or other object) against the background of distant stars. By extension, it is a method for determining the distance to the star through trigonometry, the '''stellar parallax method'''. Created by the different [[orbital positions of Earth]], the extremely small observed shift is largest at time intervals of about six months, when Earth arrives at opposite sides of the Sun in its orbit, giving a baseline (the shortest side of the triangle made by a star to be observed and two positions of Earth) distance of about two [[astronomical unit]]s between observations. The [[parallax]] itself is considered to be half of this maximum, about equivalent to the observational shift that would occur due to the different positions of Earth and the Sun, a baseline of one [[astronomical unit]] (AU).

Stellar parallax is so difficult to detect that its existence was the subject of much debate in astronomy for hundreds of years. [[Thomas Henderson (astronomer)|Thomas Henderson]], [[Friedrich Georg Wilhelm von Struve]], and [[Friedrich Bessel]] made the first successful parallax measurements in 1832–1838, for the stars [[Alpha Centauri]], [[Vega]], and [[61 Cygni|61&nbsp;Cygni]].