Speed of Light

The Physics Factbook
Edited by Glenn Elert -- Written by his students
An educational, Fair Use website

topic index | author index | special index

Bibliographic Entry Result
(w/surrounding text)
Serway, Raymond A., & Robert J. Beichner. Physics for Scientists and Engineers, Fifth Edition. USA: Saunders College Publishing, 2000. "The waves travel through a vacuum with the speed of light c, where " 3.00 × 108 m/s
"Light." World Book Encyclopedia. 2000 Edition. Chicago: World Book, 2000. "The speed of light in empty space- where atoms do not delay its travel- is 186,282 miles (299,792 kilometers) per second." 3.00 × 108 m/s
"Light, Electromagnetic Theory of." Macmillan Encyclopedia of Physics. New York: Simon & Schuster Macmillan, 1996. "… regardless of the motion of the observer, the speed of light always came out to be the same value, c = 3 × 108 m/s, with respect to the experimenter." 3.00 × 108 m/s
Fowler, Michael. The Speed of Light. University of Virginia, 1996. "… and a few years later Newton wrote in the Principia (Book I, section XIV): 'For it is now certain from the phenomena of Jupiter's satellites, confirmed by the observations of different astronomers, that light is propagated in succession (NOTE: I think this means at finite speed) and requires about seven or eight minutes to travel from the sun to the earth.'" 3.12–3.56 × 108 m/s
Historical Content of the SI: Unit of Length (Meter). National Institute of Standards and Technology. "The meter is the length of the path traveled by light in vacuum during a time interval of 1/299,792,458 of a second." 3.00 × 108 m/s

Light, which is a form of electromagnetic wave, is a phenomenon that has puzzled scientists for centuries. It was originally believed that the speed of light was not constant. Then in 1676 a Danish astronomer named Ole Romer made one of the first theories for a fixed value, c, the speed of light through free space. He theorized that, from watching the eclipse patterns of Jupiter and its moon, Io, that light travels at a finite speed due to the fact that the eclipses were seen from earth at different times than they actually occurred. The occurred latest when Io was furthest from earth and earliest when Io was closest to earth. This was due to the time required for the light to travel from Io to the earth's surface.

Presently, the speed of light has a fixed value of 299,792,458 m/s. Using Maxwell's equations, a relationship

can be derived that relates the speed of light to the fundamental constants ε0 and μ0, which are the vacuum permitivity and the permeability of free space. The speed of light can be defined as the speed it takes light to travel one meter in 1/299,792,458 of a second.

Johnny Alicea -- 2002

Bibliographic Entry Result
(w/surrounding text)
McGraw-Hill. Merrill Physics Principles and Problems. New York: McGraw-Hill, 1995. "The committee defined the speed of light in a vacuum to be exactly c = 299 792 458 m/s. For most calculations you should use c = 3.00 × 108 m/s." 299 792 458 m/s

3.00 × 108 m/s
"Speed of Light". Encyclopedia.com, 2002. "Modern electronic methods have improved this accuracy,yielding a value of 2.99792458 × 108 m (c.186,000 mi) per sec for the speed of light in a vacuum, and less for its speed in other media." 2.99792458 × 108 m/s
Perkowitz, Sidney. Empire of Light. New York: Henry Holt and Company, 1996. "The equations do not allow light to halt yet continue to undulate. If light were to remain, thought Einstein, it must always travel at 186,000 miles per second even as seen by an observer moving at the same speed (or at any speed, in any direction); to the confusion of our ingrained visceral knowledge, a rider on a light beam can never catch an adjacent beam, although he too moves at the speed of light." 3.00 × 108 m/s
Michelson Livingston, Dorothy. Master of Light: A Biography of Albert A. Michelson. New York: Scribner, 1973. "Upon his return to the United States, he determined the velocity of light to be 299,853 km s-1, a value that remained the best for a generation." 2.99853 × 108 m/s
Reference Tables for Physical Setting/Physics. Albany New York: SUNY, 2002.
Name Symbol Value
Speed of light in a vacuum c 3.00 × 108 m/s
3.00 × 108 m/s

The speed of light is so far the fastest thing known to man. Light is an electromagnetic wave. All electromagnetic waves from radio waves to x-rays travel at the speed of light. Originally the speed of light was thought to be infinite. Every century since the early 17th scientists have been perfecting the measurement of the value of the speed of light. Now modern electronic methods have improved this accuracy to a point that it has been given a set value. In 1983, the International Committee on Weights and Measurements decided to make the speed of light a defined quantity: 299 792 458 m/s (although for most calculations 3.00 × 108 m/s is sufficient).

It is said that the speed of light in a vacuum is the limiting velocity for material particles, and that no particle can be accelerated from rest to the speed of light, although it might come close. Now an objects length is measured in terms of the time required by light to travel from one end of the object to the other. While particles moving slower than that of the speed of light in a vacuum but quicker than that of light in other mediums, it will emit a faint blue light known as cherenkov radiation when they pass through the other medium, this phenomenon has been used in various applications involving elementary particles.

Matthew Stravitz -- 2002

Another quality webpage by

Glenn Elert
eglobe logo home | contact

bent | chaos | eworld | facts | physics