What the heck is the Speed of Light ?

http://www.unmuseum.org/speed.htm

Or :

Light travels at a speed of 186,000 miles a second or 700 million miles an hour. For scale, the distance from the Earth to the Moon is about 239,000 miles. This seems pretty fast and indeed theory says that nothing can travel faster than the speed of light.

In our every day lives light seems to travel from one place to another instantaneously. When we flip on the light in a room there is no delay between when we first see the bulb start glowing and when light illuminates the far corners of the chamber. Our nervous systems are much too slow to notice the rays of light that appear from the bulb and move like a wave washing over the room.

When we deal with the immense distances of space, though, even light seems slow. When astronauts were on the Moon it took over a second for the radio waves (which travel at the speed of light) carrying their voices to reach us. Light coming from the sun takes eight and one half minutes to hit Earth. (This means that if the sun were suddenly to go dark, it would take over eight minute for us to notice) Light from the nearest stars, other than the sun, takes four and a half years to get here. From the farthest stars in distant galaxies it can take billions of years for the light to arrive..

The distance light can travel in a year is called a "light year." The light year is one of the basic measures of distance for astronomy.