How fast does light go?
One of history’s greatest astronomers was named Galileo and he tried to clock the speed of light more that 300 years ago. He wanted to know how long it took the light from a lantern to cross from one hilltop to another hilltop a few miles away. The flash seemed to take no time at all and Galileo decided that light flashed across the vast reaches of space in no time at all. He was wrong.
Scientists have been trying to clock the speed of light for more than 300 years. All kinds of machines and gadgets have been invented to do the job but men of science were not satisfied with their figures until about 30 years ago. Even then they were not quite satisfied. In fact, a new experiment is just starting to check the figure we have for the speed of light. Scientist think they know the speed of light almost exactly, but they want to be as accurate as possible.
The sunbeam that kisses your nose with a pretty brown freckle traveled eight minutes and 18 seconds to reach you. The earth is more than 92 million miles from the sun and it takes light eight minutes and 18 seconds to flash across this distance from the sun to the earth. If the sunbeam missed the earth, it could go on traveling another seven hours and maybe fall upon Pluto, the lonely little planet which pedals around the outside rim of the Solar System.
Suppose we could make a sunbeam run around and around the world. It would whizz around the equator seven and a half times in a single second, a sun's light pours forth in all directions and only a shall part of it falls on the planets. The rest goes on and on into outer space. Here it travels in a vacuum with no air or solid bodies to get in its way.
Air and clouds end drifting dust slow down the speed of light a tiny fraction. So when we give the speed of light, we mean the time it takes to travel through the vacuum of space.
Its speed is about 186,300 miles a second which is roughly 669 million miles an hour. Light is the fastest traveler known and even it cannot go any faster. Suppose you loaded the sun onto a big truck and drove fast, very fast away from the earth. The sunbeams would still race towards us at the same old speed of 186,300 miles a second.
Scientists are orderly people and they like to keep their figures neat and tidy. The neatest number system goes in tens. A kilometer is equal to 1,000 meters and a meter equals 100 centimeters. On this system, light travels almost exactly 300,000 kilometers a second which equals three hundred thousand million centimeters a second.