- Light-second
A

**light-second**is aunit of length . It is defined as thedistance light travels in an absolutevacuum in onesecond or 299,792,458meter s. Note that this value is considered exact, since the meter is actually (as of1983 ) defined in terms of the light second. [*[*] It is just over 186,282*http://inms-ienm.nrc-cnrc.gc.ca/research/optical_frequency_si_e.html*] National Research Council of Canada: "Optical frequency - maintaining the SI metre"mile s and almost 10^{9}feet.A

light-minute is 60 light-seconds and alight-hour is 60 light-minutes, or 3600 light-seconds. Alight-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 planetEarth 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 satellite s are typically 0.001334s (low earth orbit ) to 0.1194s (geostationary orbit )

* The average distance from the Earth to theMoon is about 1.282 light-seconds.

* The diameter of theSun is about 4.643 light-seconds.

* The average distance from the Earth to the Sun (i.e. 1astronomical 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