# Light-second

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Light-second

A light-second is a unit of length. It is defined as the distance light travels in an absolute vacuum in one second or 299,792,458 meters. Note that this value is considered exact, since the meter is actually (as of 1983) defined in terms of the light second. [ [http://inms-ienm.nrc-cnrc.gc.ca/research/optical_frequency_si_e.html] National Research Council of Canada: "Optical frequency - maintaining the SI metre"] It is just over 186,282 miles and almost 109 feet.

A light-minute is 60 light-seconds and a light-hour is 60 light-minutes, or 3600 light-seconds. A light-year is 31,557,600 light-seconds.

Some distances in light seconds:

* The mean diameter of the Earth is about 0.0425 light-seconds.
* The mean distance, over land, between opposite sides of the planet Earth is about 0.0668 light-seconds (which also means that communications between opposite sides of the planet, taking a circumferential path, can never travel faster than about 67 milliseconds).
* Communications satellites are typically 0.001334s (low earth orbit) to 0.1194s (geostationary orbit)
* The average distance from the Earth to the Moon is about 1.282 light-seconds.
* The diameter of the Sun is about 4.643 light-seconds.
* The average distance from the Earth to the Sun (i.e. 1 astronomical unit) is 499.0 light-seconds, or 8.317 light-minutes.

It is also possible to add diminutive suffixes, such as the light-nanosecond, equal to almost exactly 30 cm (11.8 in or nearly a foot).

References

ee also

* Light-day
* Light-hour
* Light-minute
* Light-month
* Light-week
* Light-year
* Speed of light
* 1 E8 m

Wikimedia Foundation. 2010.

### Look at other dictionaries:

• light second —    a unit of distance equal to the distance light travels in a vacuum in one second. In accordance with the official definition of the meter, this distance is exactly 299 792 458 meters (about 186 282.4 miles). Similarly, a light minute is 60… …   Dictionary of units of measurement

• light second — noun the distance light travels in a vacuum in one second; approximately 300,000 kilometers • Hypernyms: ↑astronomy unit • Part Holonyms: ↑light year, ↑light year …   Useful english dictionary

• light second — noun A unit of length equal to the distance light travels in one second …   Wiktionary

• Light cone — in 2D space plus a time dimension. A light cone is the path that a flash of light, emanating from a single event (localized to a single point in space and a single moment in time) and traveling in all directions, would take through spacetime. If… …   Wikipedia

• Light-year — For other uses, see Light year (disambiguation). Image showing the scale of a light year (outer shell) and a light month (inner shell) surrounding the Sun compared to Comet 1910 A1 s orbit (yellow line) and Comet Hyakutake s orbit (orange line).… …   Wikipedia

• light-year — noun the distance that light travels in a vacuum in 1 year; 5.88 trillion miles or 9.46 trillion kilometers • Syn: ↑light year • Hypernyms: ↑astronomy unit • Part Meronyms: ↑light hour, ↑light minute, ↑light second …   Useful english dictionary

• Light-minute — A light minute (also written light minute) is a unit of length. It is defined as the distance light travels in an absolute vacuum in one minute or 17,987,547,480 metres ( 18 Gm). Note that this value is exact, since the metre is actually defined… …   Wikipedia

• Light-week — A light week (also written light week) is a unit of length. It is defined as the distance light travels in an absolute vacuum in one week (seven days of 86,400 seconds each) or 181,314,478,598,400 metres ( 181 Tm).Note that this value is exact,… …   Wikipedia

• Light-day — A light day (also written light day) is a unit of length. It is defined as the distance light travels in an absolute vacuum in one day (of 86,400 seconds) or 25,902,068,371,200 metres ( 26 Tm).Note that this value is exact, since the metre is… …   Wikipedia

• Light-month — A light month (also written light month) is a unit of length. It is defined as the distance light travels in an absolute vacuum in one full month (thirty days of 86,400 seconds each) or 777,062,051,136,000 metres ( 777 Tm). Explanation Note that… …   Wikipedia