Light year: Difference between revisions
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Similar units are the [[light second]], [[light minute]], [[light hour]], [[light day]], [[light week]], [[light month]]. As opposed to the light year, whose value more or less depends on the definition of [[year]], the values of all these units are defined exactly. | Similar units are the [[light second]], [[light minute]], [[light hour]], [[light day]], [[light week]], [[light month]]. As opposed to the light year, whose value more or less depends on the definition of [[year]], the values of all these units are defined exactly. | ||
=== | |||
* [[velocity]] of [[light]] in [[vacuum]]: 299,792, | ===Numerical value=== | ||
* [[velocity]] of [[light]] in [[vacuum]]: 299,792,458 m/s <ref>Review of Particle Physics | |||
[http://stacks.iop.org/JPhysG/33/1 Particle Data Group: W.-M. Yao ''et al.'', J. Phys. G 33, 1 (2006).]</ref> ([[meter]]s/[[second]]) | |||
* one [[julian year]] = 365.25 days = 31,557,600 s | * one [[julian year]] = 365.25 days = 31,557,600 s | ||
* 1ly = 9,460,730, | * 1ly = 9,460,730,472,580,800 m | ||
===Comparison to other Units=== | ===Comparison to other Units=== | ||
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* 1 [[parsec]] = 3.2616 ly | * 1 [[parsec]] = 3.2616 ly | ||
* 1 [[astronomical unit| AU]] = 15.8×10<sup>-6</sup> ly | * 1 [[astronomical unit| AU]] = 15.8×10<sup>-6</sup> ly | ||
* 1 ly = 9,460,730, | * 1 ly = 9,460,730,472,580.800 [[km]] = 9.4607304 * 10<sup>12</sup> [[km]] | ||
* 1 ly = 5, | * 1 ly = 5,878,625,373,183.607 [[mi]]<ref>1 mi = 1609.344 m</ref> = 5.878625 * 10<sup>15</sup> [[mi]] | ||
* 1 ly = 31,039,141, | * 1 ly = 31,039,141,970,409,448.818 [[ft]]<ref> 1 ft = 0.3048 m</ref> = 31.039142 * 10<sup>15</sup> [[ft]] | ||
* 1 ly = 10,346,380, | * 1 ly = 10,346,380,656,803,149.606 [[yd]]<ref> 1 yd = 0.9144 m</ref> = 10.346381 * 10<sup>15</sup> [[yd]] | ||
===Distances in Light-Years=== | ===Distances in Light-Years=== | ||
* the average distance between [[earth]] and [[moon]] is about 1.3 [[light seconds]] | * the average distance between [[earth]] and [[moon]] is about 1.3 [[light seconds]] | ||
* the average distance between [[earth]] and [[sun]] is about 499 [[light seconds]] or 8.3 [[light minutes]] | * the average distance between [[earth]] and [[sun]] is about 499 [[light seconds]] or 8.3 [[light minutes]] | ||
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* the diameter of our [[galaxy]] is about 100,000 light years | * the diameter of our [[galaxy]] is about 100,000 light years | ||
* the distance to a galaxy called [[Andromeda nebular]] is about 2.4 to 2.7 million light years | * the distance to a galaxy called [[Andromeda nebular]] is about 2.4 to 2.7 million light years | ||
===Notes=== | |||
<div class="references-2column"> | |||
<references /> | |||
</div> | |||
===External links=== | |||
* [http://pdg.lbl.gov Particle Data Group & WWW edition of ''Review of Particle Physics''] | |||
* [http://stacks.iop.org/JPhysG/33/1 2006 ''Review of Particle Physics'' in printed layout] | |||
[[Category:CZ Live|Light year]] | [[Category:CZ Live|Light year]] | ||
[[Category:Astronomy Workgroup|Light year]] | [[Category:Astronomy Workgroup|Light year]] | ||
Revision as of 12:51, 7 October 2007
The light year (symbol: ly) is the distance that the light travels in vacuum in one year. Although one might think that one year is defined as the time for the Earth to complete one revolution of its orbit of the Sun, there are still several definitions depending on the frame of reference. According to the recommendations of the International Astronomical Union (IAU), the Julian year, which has a length of 365.25 days or 31,557,600 seconds, shall be used.
The light year is a unit of distance larger than an astronomical unit (AU). It is commonly used to measure interstellar distances, where other units of measure are too small. It is rarely used in interplanetary distances, because it is too large to be useful.
Similar units are the light second, light minute, light hour, light day, light week, light month. As opposed to the light year, whose value more or less depends on the definition of year, the values of all these units are defined exactly.
Numerical value
- velocity of light in vacuum: 299,792,458 m/s [1] (meters/second)
- one julian year = 365.25 days = 31,557,600 s
- 1ly = 9,460,730,472,580,800 m
Comparison to other Units
- 1 parsec = 3.2616 ly
- 1 AU = 15.8×10-6 ly
- 1 ly = 9,460,730,472,580.800 km = 9.4607304 * 1012 km
- 1 ly = 5,878,625,373,183.607 mi[2] = 5.878625 * 1015 mi
- 1 ly = 31,039,141,970,409,448.818 ft[3] = 31.039142 * 1015 ft
- 1 ly = 10,346,380,656,803,149.606 yd[4] = 10.346381 * 1015 yd
Distances in Light-Years
- the average distance between earth and moon is about 1.3 light seconds
- the average distance between earth and sun is about 499 light seconds or 8.3 light minutes
- the diameter of our solar system is about 150 light hours
- the Oort cloud is approximately 2 light years in diameter.
- the nearest star, Proxima Centauri, has a distance of about 4.2 light years
- the diameter of our galaxy is about 100,000 light years
- the distance to a galaxy called Andromeda nebular is about 2.4 to 2.7 million light years
Notes
- ↑ Review of Particle Physics Particle Data Group: W.-M. Yao et al., J. Phys. G 33, 1 (2006).
- ↑ 1 mi = 1609.344 m
- ↑ 1 ft = 0.3048 m
- ↑ 1 yd = 0.9144 m