Light year

Article

January 27, 2022

A light year is the distance that light travels in one year. It should be noted that the light year is a unit of distance, not time. For fast calculations, the speed of light is considered to be equal to 3 × 108 m / s, and since it has 60 × 60 × 24 × 365 31,536,000 seconds in one year, using the formula s v ⋅ t {\ displaystyle s v \ cdot t} , the approximate light year is calculated - 9,460,800,000,000,000 meters. The exact light speed is 2.999724580 × 108 m / s, so the light year has 9,454,254,955,488,000 meters, or a little less than nine and a half billion kilometers. However, for a complete calculation, it should be taken into account that an astronomical year (solar year) has 365 days, 5 hours, 48 ​​minutes and 45 seconds, so the number of seconds in a year is actually 31,556,925. In that case, the light year is 9,460,528,112,671,650 meters. Often in astronomy, instead of the light year, a unit of similar size, the parsec, is used. One light year is 0.307 parsecs.

Definitions

According to the IAU definition, a light year is the product of the Julian year (365.25 days as opposed to the Gregorian year of 365.2425 days) and the speed of light (299,792,458 m / s). Both of these values ​​are included in the IAU (1976) Astronomical Constants System, which has been used since 1984. The following conversions can be derived from this. The IAU recognized abbreviation for light year is ly, although other standards such as ISO 80000 use "l.y." and localized abbreviations are common, such as "al" in French (from année-lumière), Spanish (from año luz) and Italian (from anno luce), "Lj" in German (from Lichtjahr), etc. Prior to 1984, tropical year (not Julian) and measured (undefined) speed of light were used in the IAU (1964) Astronomical Constants System, used from 1968 to 1983. Simon Newcomb's J1900.0 product, average tropical year of 31,556,925 , 9747 ephemeris seconds and a speed of light of 299,792.5 km / s produced a light year of 9,460,530 × 1015 m (rounded to seven significant digits in the speed of light) is present in several modern sources which is probably derived from an old source, such as reference work KV Alena from 1973. Astrophysical Quantities, which was updated in 2000, including the above-mentioned IAU value (1976) (abbreviated to 10 significant digits). Other high-precision values ​​are not derived from a coherent IAU system. Value

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