Light Year

Distance between two destinations in space are extreme and normal measurements of length are inadequate. All space faring societies have their own way of expressing these. Terrans often use the measurement Light Year (see below) The modern Standard Union measurement is called the SPUL (SPatial Unit of Length ) based on the time the Pulse of 14 known Pulsars in the Milky Way Galaxy take to reach Pluribus (middled value) and the tame it takes in (Union Standard Time). = 1 SPUL (it works out to almost exactly 100 Light Years) So in general Old Light Year distances / 100 = SPUL

A light-year, also light year or lightyear (symbol: ly), is a unit of length equal to just under 10 1000000000000 (number) [million kilometres (or about 6 million million miles). As defined by the International Astronomical Union (IAU)(Earth Based Pre Astro Organization), a light-year is the distance that light travels in a vacuum in one Julian year.

The light-year is mostly used to express distances to stars and other distances on a galactic scale, especially in non-specialist and popular science publications. The preferred unit in astrometry is the parsec (approximately 3.26 light-years), because it can be more easily derived from, and compared with, observational data.[1]

Note that the light-year is a measure of distance. It is not a measure of time, for which it is sometimes mistaken.

Numerical Value

1 light-year = 9460730472580800 metres (exactly)

≈ 5878625 million miles

≈ 63241.077 astronomical units

≈ 0.306601 parsecs

The figures above are based on a Julian year (not Gregorian year) of exactly 365.25 days (each of exactly 86400 SI seconds, totalling 31557600 seconds)[2] and a defined speed of light of 299792458 m/s, both included in the IAU (1976) System of Astronomical Constants, used since 1984.[3]

[edit]Other values

Before 1984, the tropical year (not the Julian year) and a measured (not defined) speed of light were included in the IAU (1964) System of Astronomical Constants, used from 1968 to 1983.[4] The product of Simon Newcomb's J1900.0 mean tropical year of 31556925.9747 ephemeris seconds and a speed of light of 299792.5 km/s produced a light-year of 9.460530×1015 m (rounded to the seven significant digits in the speed of light) found in several modern sources[5][6][7] was probably derived from an old source such as C. W. Allen's 1973 Astrophysical Quantities reference work,[8] which was updated in 2000.[9]

Other high-precision values are not derived from a coherent IAU system. A value of 9.460536207×1015 m found in some modern sources[10][11] is the product of a mean Gregorian year of 365.2425 days (31556952 s) and the defined speed of light (299792458 m/s). Another value, 9.460528405×1015 m,[12][13] is the product of the J1900.0 mean tropical year and the defined speed of light.