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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).
Stellar parallax is the apparent shift of position 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 .
Concept art for the TAU spacecraft, 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 ...
Astronomers and natural philosophers before divided the lights in the sky into two groups. One group contained the fixed stars, which appear to rise and set but keep the same relative arrangement over time, and show no evident stellar parallax, which is a change in
The lower diagram shows the 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 number is wrong; originally announced in 1891, the figure was corrected in 1910 to 40 ly (60 mas). From 1891 to 1910, it had been thought this was the star with the smallest known parallax, hence the most distant star whose distance was known. Prior to 1891, Arcturus had previously been recorded of having a parallax of 127 mas.
A simplified illustration of the parallax of an object against a distant background due to a perspective shift. When viewed from "Viewpoint A", the object appears to be in front of the blue square. When the viewpoint is changed to "Viewpoint B", the object appears to have moved in front of the red square. This animation is an example of parallax.
The measurement of stellar parallax of nearby stars provides a fundamental baseline in the cosmic distance ladder that is used to measure the scale of the Universe. Parallax measurements of nearby stars provide an absolute baseline for the properties of more distant stars, as their properties can be compared.