Gerard Harrington, age 12, of Roslindale, Mass., for his question:
How long does it take the sun's rays to reach the earth?
A beam of light whisks along at 11,160,000 miles per hour. If it could bend, it could zoom around the equator seven times in a single second and go 11,000 miles, or almost half way around an eighth trip. Light, however, cannot bend around in circles.
Nothing in the universe travels faster than a sunbeam. Several cosmic travelers can equal it, but none can out race it. After years of patient measuring, astronomers now estimate the speed of light to be about 186,000 miles per second. Sunlight zooms toward us at the same speed as the light from the twinkling stars. Moonlight is sunlight reflected from the face of the moon. It travels to the moon at 186,000 miles a second and at the same speed from the moon to the earth. The planets also shed reflected sunlight toward us.
Sunbeams of radiant energy pour forth in straight lines from the entire surface of our sun, fanning outward as they go. About two billionths of the immense output happens to strike our planet. These sunbeams have crossed about 93 million miles of space to reach us this is the average distance between the earth and the sun. It takes them somewhat less than six seconds to travel each million miles.
It takes eight minutes and 18 seconds for light to travel the 93 million miles between the earth and the sun. The sunbeam that just arrived to plant a freckle on your nose set out from the sun precisely 498 seconds ago. If that same sunbeam had happened to be angled on a course toward Pluto, it would take more than five hours to get there. A beam of light from a distant star takes about 11.5 hours to cross the widest span of the solar system.
The speed of light shows us a staggering picture of the immense universe. It takes 80,000 years for a non stop beam to cross our galaxy from side to side. The light we see from sirius, the brilliant dog star, set out toward us more than four years ago. This neighboring star is more than eight light years away from us. Some of the stars we see are at distances of 20, 30 and even hundreds of light years. Telescopes photograph stars at millions of light years. Some of those distant stars may have died ages before their light reached the earth.
The light from a candle or search beam, from the sun or from a distant star travels in straight lines at a steady speed of 186,000 miles per second. Sunlight takes about eight minutes and 19.5 seconds to reach the face of the full moon. Since the average distance between us and the moon is 235,000 miles, you can figure just how long it takes the light of the moon to reach the earth.