Light second
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "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.^[1] 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

1. ^ [1] National Research Council of Canada: Optical frequency - maintaining the SI metre

See also

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