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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, which is approximately 5.88 trillion mi.
The calculated stellar distance will be in the same measurement unit as used in Distance earth-sun (e.g. if Distance earth-sun = 1 au, unit for Distance star is in astronomical units; if Distance earth-sun = 1.5813 × 10 −5 ly, unit for Distance star is in light-years). The length of the parsec used in IAU 2015 Resolution B2 [11] (exactly ...
The astronomical unit is too small to be convenient for interstellar distances, where the parsec and light-year are widely used. The parsec (parallax arcsecond) is defined in terms of the astronomical unit, being the distance of an object with a parallax of 1″. The light-year is often used in popular works, but is not an approved non-SI unit ...
20 Pm – 2.11 light-years – maximum extent of influence of the Sun's gravitational field [citation needed] 30.9 Pm – 3.26 light-years – 1 parsec; 39.9 Pm – 4.22 light-years – distance to Proxima Centauri (nearest star to Sun) 81.3 Pm – 8.59 light-years – distance to Sirius; 94.6 Pm – 1 light-decade
astronomical unit au. Defined as 149 597 870 700 m. [16] Approximately the distance between the Earth and Sun. light-year ly ≈ 9 460 730 472 580.8 km. The distance that light travels in a vacuum in one Julian year. [17] parsec pc ≈ 30 856 775 814 671.9 km or about 3.261 56 ly; Hubble length 14.4 billion light-years or 4.55 gigaparsecs
The amount of shift is quite small, even for the nearest stars, measuring 1 arcsecond for an object at 1 parsec's distance (3.26 light-years), and thereafter decreasing in angular amount as the distance increases. Astronomers usually express distances in units of parsecs (parallax arcseconds); light-years are used in popular media.
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).
d - in ly = light-year; d - in pc = parsec; d - in kpc = kiloparsec (1000 pc) ... M E, M E - mass of Earth; M J ... Astronomical symbols;