Just as the second forms the basis for other units of time, the light-second can form the basis for other units of length, ranging from the light-nanosecond (299.8 mm or just under one international foot) to the light-minute, light-hour and light-day, which are sometimes used in popular science publications. The more commonly used light-year is also currently defined to be equal to precisely 31557600 light-seconds, since the definition of a year is based on a Julian year (not the Gregorian year) of exactly 365.25 days, each of exactly 86400SI seconds.[1]
Communications signals on Earth rarely travel at precisely the speed of light in free space.[citation needed] Distances in fractions of a light-second are useful for planning telecommunications networks.
One light-nanosecond is almost 300 millimetres (299.8 mm, 5 mm less than one foot[2]), which limits the speed of data transfer between different parts of a large computer.
One light-microsecond is about 300 metres.
The mean distance, over land, between opposite sides of the Earth is 66.8 light-milliseconds.
Communications satellites are typically 1.337 light-milliseconds[citation needed] (low Earth orbit) to 119.4 light-milliseconds (geostationary orbit) from the surface of the Earth. Hence there will always be a delay of at least a quarter of a second in a communication via geostationary satellite (119.4 ms times 2); this delay is just perceptible in a transoceanic telephone conversation routed by satellite. The answer will also be delayed with a quarter of a second and this is clearly noticeable during interviews or discussions on TV when sent over satellite.
Use in astronomy
The yellow shell indicating one light-day distance from the Sun compares in size with the positions of Voyager 1 and Pioneer 10 (red and green arrows respectively). It is larger than the heliosphere's termination shock (blue shell) but smaller than Comet Hale-Bopp's orbit (faint orange ellipse below). Click on the image for a larger view and links to other scales.
The faint yellow sphere centred on the Sun has a radius of one light-minute. For comparison, sizes of Rigel (the blue star in the top left) and Aldebaran (the red star in the top right) are shown to scale. The large yellow ellipse represents Mercury's orbit.
The light-second is a convenient unit for measuring distances in the inner Solar System, since it corresponds very closely to the radiometric data used to determine them. (The match is not exact for an Earth-based observer because of a very small correction for the effects of relativity.) The value of the astronomical unit (roughly the distance between Earth and the Sun) in light-seconds is a fundamental measurement for the calculation of modern ephemerides (tables of planetary positions). It is usually quoted as "light-time for unit distance" in tables of astronomical constants, and its currently accepted value is 499.004786385(20) s.[3][4]
The mean diameter of Earth is about 0.0425 light-seconds.
The average distance between Earth and the Moon (the lunar distance) is about 1.282 light-seconds.
The diameter of the Sun is about 4.643 light-seconds.
The average distance between Earth and the Sun (the astronomical unit) is 499.0 light-seconds.
Multiples of the light-second can be defined, although apart from the light-year, they are more used in popular science publications than in research works. For example, a light-minute is 60 light-seconds, and the average distance between Earth and the Sun is 8.317 light-minutes.
Unit
Definition
Equivalent distance in
Example
m
km
miles
light-second
299792458 m
2.998×105 km
1.863×105 mi
Average distance from the Earth to the Moon is about 1.282 light-seconds
light-minute
60 light-seconds
17987547480 m
1.799×107 km
1.118×107 mi
Average distance from the Earth to the Sun is 8.317 light-minutes
^Standish, E. M. (1998). (PDF). JPL IOM 312.F-98-048. Archived from the original (PDF) on 2012-02-20..
^McCarthy, Dennis D.; Petit, Gérard, eds. (2004). "IERS Conventions (2003)". IERS Technical Note No. 32. Frankfurt: Bundesamts für Kartographie und Geodäsie. ISBN3-89888-884-3.
January 06, 2023
light, second, light, second, unit, length, useful, astronomy, telecommunications, relativistic, physics, defined, distance, that, light, travels, free, space, second, equal, exactly, 299792, metres, 983571, unit, oflengthconversions1, light, second, equal, un. The light second is a unit of length useful in astronomy telecommunications and relativistic physics It is defined as the distance that light travels in free space in one second and is equal to exactly 299792 458 metres 983571 056 ft Light secondUnit oflengthConversions1 light second in is equal to SI units 299792 458 m astronomical units 0 0020040 AU 3 1688 10 8 ly 9 7156 10 9 pc imperial US units 186282 miJust as the second forms the basis for other units of time the light second can form the basis for other units of length ranging from the light nanosecond 299 8 mm or just under one international foot to the light minute light hour and light day which are sometimes used in popular science publications The more commonly used light year is also currently defined to be equal to precisely 31557 600 light seconds since the definition of a year is based on a Julian year not the Gregorian year of exactly 365 25 days each of exactly 86400 SI seconds 1 Contents 1 Use in telecommunications 2 Use in astronomy 3 See also 4 ReferencesUse in telecommunications EditCommunications signals on Earth rarely travel at precisely the speed of light in free space citation needed Distances in fractions of a light second are useful for planning telecommunications networks One light nanosecond is almost 300 millimetres 299 8 mm 5 mm less than one foot 2 which limits the speed of data transfer between different parts of a large computer One light microsecond is about 300 metres The mean distance over land between opposite sides of the Earth is 66 8 light milliseconds Communications satellites are typically 1 337 light milliseconds citation needed low Earth orbit to 119 4 light milliseconds geostationary orbit from the surface of the Earth Hence there will always be a delay of at least a quarter of a second in a communication via geostationary satellite 119 4 ms times 2 this delay is just perceptible in a transoceanic telephone conversation routed by satellite The answer will also be delayed with a quarter of a second and this is clearly noticeable during interviews or discussions on TV when sent over satellite Use in astronomy Edit The yellow shell indicating one light day distance from the Sun compares in size with the positions of Voyager 1 and Pioneer 10 red and green arrows respectively It is larger than the heliosphere s termination shock blue shell but smaller than Comet Hale Bopp s orbit faint orange ellipse below Click on the image for a larger view and links to other scales The faint yellow sphere centred on the Sun has a radius of one light minute For comparison sizes of Rigel the blue star in the top left and Aldebaran the red star in the top right are shown to scale The large yellow ellipse represents Mercury s orbit The light second is a convenient unit for measuring distances in the inner Solar System since it corresponds very closely to the radiometric data used to determine them The match is not exact for an Earth based observer because of a very small correction for the effects of relativity The value of the astronomical unit roughly the distance between Earth and the Sun in light seconds is a fundamental measurement for the calculation of modern ephemerides tables of planetary positions It is usually quoted as light time for unit distance in tables of astronomical constants and its currently accepted value is 499 004786 385 20 s 3 4 The mean diameter of Earth is about 0 0425 light seconds The average distance between Earth and the Moon the lunar distance is about 1 282 light seconds The diameter of the Sun is about 4 643 light seconds The average distance between Earth and the Sun the astronomical unit is 499 0 light seconds Multiples of the light second can be defined although apart from the light year they are more used in popular science publications than in research works For example a light minute is 60 light seconds and the average distance between Earth and the Sun is 8 317 light minutes Unit Definition Equivalent distance in Examplem km mileslight second 299792 458 m 2 998 105 km 1 863 105 mi Average distance from the Earth to the Moon is about 1 282 light secondslight minute 60 light seconds 17987 547 480 m 1 799 107 km 1 118 107 mi Average distance from the Earth to the Sun is 8 317 light minuteslight hour 60 light minutes 3600 light seconds 1079 252 848 800 m 1 079 109 km 6 706 108 mi The Perihelion of Saturn s orbit is about 1 25 light hourslight day 24 light hours 86400 light seconds 25902 068 371 200 m 2 590 1010 km 1 609 1010 mi Voyager 1 is currently 0 9 light days from the Sunlight week 7 light days 604800 light seconds 181314 478 598 400 m 1 813 1011 km 1 127 1011 mi The Oort cloud is thought to extend between 41 and 82 light weeks out from the Sunlight month 30 light days 2 592 10 6 light seconds 7 771 1014 m 7 771 1011 km 4 828 1011 milight year 365 25 light days 31557 600 light seconds 9460 730 472 580 800 m 9 461 1012 km 5 879 1012 mi Proxima Centauri is the nearest star to the Sun about 4 24 light years awaySee also Edit100 megametres Geometrized unit system Light yearReferences Edit IAU Recommendations concerning Units Archived 2007 02 16 at the Wayback Machine David Mermin suggested one light nanosecond might be called a phoot at page 22 of It s About Time 2005 Princeton University Press Standish E M 1998 JPL Planetary and Lunar Ephemerides DE405 LE405 PDF JPL IOM 312 F 98 048 Archived from the original PDF on 2012 02 20 McCarthy Dennis D Petit Gerard eds 2004 IERS Conventions 2003 IERS Technical Note No 32 Frankfurt Bundesamts fur Kartographie und Geodasie ISBN 3 89888 884 3 Retrieved from https en wikipedia org w index php title Light second amp oldid 1114655796, wikipedia, wiki, book, books, library,
