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Parallax is a displacement or difference in the apparent position of an object viewed along two different lines of sight and is measured by the angle or half-angle of inclination between those two lines. [1] [2] Due to foreshortening, nearby objects show a larger parallax than farther objects, so parallax can be used to determine distances.
A parsec is the distance from the Sun to an astronomical object that has a parallax angle of one arcsecond (not to scale). The parsec (symbol: pc) is a unit of length used to measure the large distances to astronomical objects outside the Solar System, approximately equal to 3.26 light-years or 206,265 astronomical units (AU), i.e. 30.9 trillion kilometres (19.2 trillion miles).
The lower diagram shows an equal angle swept by the Sun in a geostatic model. A similar diagram can be drawn for a star except that the angle of parallax would be minuscule. The most important fundamental distance measurements in astronomy come from trigonometric parallax, as applied in the stellar parallax method. As the Earth orbits the Sun ...
This is a compilation of symbols commonly used in astronomy, particularly professional astronomy. Age (stellar) τ - age ... parallax; J - epoch; α - Right Ascension ...
Stellar parallax is so difficult to detect that its existence was the subject of much debate in astronomy for hundreds of years. 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 .
In astronomy, the disparity between different locations on the Earth can be used to determine various celestial parallax, and Earth's orbit can be used for stellar parallax. Definition [ edit ]
In spherical astronomy, the parallactic angle is the angle between the great circle through a celestial object and the zenith, and the hour circle of the object. [1] It is usually denoted q. In the triangle zenith—object—celestial pole, the parallactic angle will be the position angle of the zenith at the celestial object.
Parallax, in point-lens events, can best be measured for long-timescale events, with a large , i..e. from slow-moving, low mass lenses, which are close to the observer. If the source star is a binary star, then it too will have additional relative motion, which can also cause detectable changes in the light curve.