The speed of light in a vacuum is exactly equal to 299,792,458 metres per second (approximately 186,282 miles per second). This exact speed is a definition, not a measurement, as the metre is defined in terms of the speed of light and not vice versa. According to standard modern physical theory, all electromagnetic radiation, including visible light, propagates (or moves) at a constant speed in vacuo, known as the speed of light, which is a physical constant denoted as c. According to the theory of special relativity, all observers will measure the speed of light as being the same, regardless of the reference frame of the observer or the velocity of the object emitting the light.

Read the rest of this article: http://en.wikipedia.org/wiki/Speed_of_light

Today's selected anniversaries:

1787 Mozart's opera Don Giovanni received its first performance in Prague. (http://en.wikipedia.org/wiki/Don_Giovanni)

1886 New York City office workers spontaneously "invented" the ticker tape parade. (http://en.wikipedia.org/wiki/ticker_tape_parade)

1923 Mustafa Kemal Atat�rk became the first President of the Republic of Turkey, a new nation founded from remnants of the Ottoman Empire. (http://en.wikipedia.org/wiki/Kemal_Atat%EF%BF%BDrk)

1945 The first ballpoint pens went on sale at a department store in New York City for US$12.50 each. (http://en.wikipedia.org/wiki/Ballpoint_pen)

1956 The Suez Crisis began: Israel invaded the Sinai Peninsula and pushed Egyptian forces back toward the Suez Canal. (http://en.wikipedia.org/wiki/Suez_Crisis)

1998 The Truth and Reconciliation Commission presented its report on Apartheid in South Africa. (http://en.wikipedia.org/wiki/Truth_and_Reconciliation_Commission)

Wikiquote of the day:

"We're just being ourselves and having fun playing baseball. The biggest thing is when people look at our team, they can see that we're having a lot of fun." ~ Johnny Damon (http://en.wikiquote.org/wiki/Johnny_Damon)