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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 .
This number is likely much higher, due to the sheer number of stars needed to be surveyed; a star approaching the Solar System 10 million years ago, moving at a typical Sun-relative 20–200 kilometers per second, would be 600–6,000 light-years from the Sun at present day, with millions of stars closer to the Sun.
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).
Based upon an annual parallax shift of 0.00632 arcseconds, [1] the distance to this system is roughly 520 light years. This is a single-lined spectroscopic binary system, [ 9 ] which means that only the absorption line features of one of the components can be distinguished.
To the naked eye Acrux appears as a single star, but it is actually a multiple star system containing six components. Through optical telescopes, Acrux appears as a triple star, whose two brightest components are visually separated by about 4 arcseconds and are known as Acrux A and Acrux B, α 1 Crucis and α 2 Crucis, or α Crucis A and α ...
Overview over the radio structure of Centaurus A. The whole radio emitting region extends about 1.8 million light years (about 8° degrees in the sky). Through observations with the VLBI technique structures of the jet and the core smaller than a light year could be resolved (corresponding to a resolution of 0.68 x 0.41 milli-arcseconds. [53])
The Andromeda Galaxy is approximately 2.5 million light-years away. 3 × 10 6 ly: The Triangulum Galaxy , at about 3 million light-years away, is the most distant object visible to the naked eye. 5.9 × 10 7 ly: The nearest large galaxy cluster, the Virgo Cluster, is about 59 million light-years away. 1.5 × 10 8 – 2.5 × 10 8 ly
HD 141569 is an isolated [5] Herbig Ae/Be star [6] of spectral class A2Ve [7] approximately 364 light-years away in the constellation of Libra. The primary star has two red dwarf companions (orbiting each other) at about nine arcseconds. In 1999, a protoplanetary disk was discovered around the star.