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A light-year, alternatively spelled light year (ly or lyr[3]), is a unit of length used to express astronomical distances and is equal to exactly 9,460,730,472,580.8 km (Scientific notation: 9.4607304725808 × 10 12 km), which is approximately 5.88 trillion mi.
3.261 56 ly. 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). [a] The parsec unit is obtained by the use of parallax and trigonometry ...
Stellar parallax is most often measured using annual parallax, defined as the difference in position of a star as seen from Earth and Sun, i.e. the angle subtended at a star by the mean radius of Earth's orbit around the Sun. The parsec (3.26 light-years) is defined as the distance for which the annual parallax is 1 arcsecond.
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.
Distance of the outer limit of Oort cloud from the Sun (estimated, corresponds to 1.2 light-years) – Parsec: 206,265 – One parsec. The parsec is defined in terms of the astronomical unit, is used to measure distances beyond the scope of the Solar System and is about 3.26 light-years: 1 pc = 1 au/tan(1″) [6] [61] Proxima Centauri: 268,000 ...
Ordinary (baryonic) matter (4.9%) Dark matter (26.8%) Dark energy (68.3%) [6] The observable universe is a ball-shaped region of the universe consisting of all matter that can be observed from Earth or its space-based telescopes and exploratory probes at the present time; the electromagnetic radiation from these objects has had time to reach ...
Alpha Centauri (α Centauri, α Cen, or Alpha Cen) is a triple star system in the southern constellation of Centaurus. It consists of three stars: Rigil Kentaurus (α Centauri A), Toliman (α Centauri B), and Proxima Centauri (α Centauri C). [14] Proxima Centauri is the closest star to the Sun at 4.2465 light-years (1.3020 pc).
Since 1894, irregularities have been tentatively observed in the orbits of Sirius A and B with an apparent periodicity of 6–6.4 years. A 1995 study concluded that such a companion likely exists, with a mass of roughly 0.05 solar mass—a small red dwarf or large brown dwarf , with an apparent magnitude of more than 15, and less than 3 ...