Light year: Difference between revisions
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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 dependig on the frame of reference. According to the recommendations of the [[International Astronomical Union]] (IAU) the [[ | 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 dependig 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]]. 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. | The light year is a unit of distance larger than an [[astronomical unit]]. 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. | ||
== numerical value == | == numerical value == | ||
* [[velocity]] of [[light]] in [[vacuum]]: 2.99792456 * 10<sup>8</sup> [[meter]]s/[[second]] | * [[velocity]] of [[light]] in [[vacuum]]: 2.99792456 * 10<sup>8</sup> m/s ([[meter]]s/[[second]]) | ||
* one [[ | * one [[julian year]] = 365.25 days = 31557600 s | ||
* 1ly = 9.460730409 * 10<sup>15</sup>m | * 1ly = 9.460730409 * 10<sup>15</sup>m | ||
===Comparison to other Units=== | ===Comparison to other Units=== | ||
===Distances in Light-Years=== | ===Distances in Light-Years=== | ||
* the average distance between earth and moon are about 1.3 light seconds | |||
* the average distance between earth and sun are about 500 light seconds or 8.3 light minutes | |||
* the diameter of out [[solar system]] is about 150 light hours | |||
* 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 Andrromeda nebular is about 2.4 to 2.7 million light years | |||
[[Category:CZ Live|Light year]] | |||
[[Category:Astronomy Workgroup|Light year]] | |||
Revision as of 15:04, 14 September 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 dependig 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. 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.
numerical value
- velocity of light in vacuum: 2.99792456 * 108 m/s (meters/second)
- one julian year = 365.25 days = 31557600 s
- 1ly = 9.460730409 * 1015m
Comparison to other Units
Distances in Light-Years
- the average distance between earth and moon are about 1.3 light seconds
- the average distance between earth and sun are about 500 light seconds or 8.3 light minutes
- the diameter of out solar system is about 150 light hours
- 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 Andrromeda nebular is about 2.4 to 2.7 million light years