How far is a light-year?
If you scaled the distance between our Earth and sun to the length of a single inch, then a light-year on this scale would equal one mile. (NASA)
JB: This is Earth and Sky. When speaking of stars and galaxies, astronomers talk about light-years.
DB: A light-year is the distance that starlight travels in a single year. Light travels at 300,000 kilometers per second – that’s 186,000 miles a second. It’s like circling Earth’s equator 7 and 1/2 times in one second.
JB: Now multiply that number by the number of seconds in a year. And that’s a light-year – 9 and 1/2 trillion kilometers – nearly 6 trillion miles. It’s difficult to comprehend such humongous numbers. So the 20th century astronomer Robert Burnham Jr. came up with an ingenious way to portray a light-year, relating it to our distance from the sun.
DB: The sun-Earth distance is called one astronomical unit by astronomers. There are about 63,000 astronomical units in one light-year. By coincidence, there are also 63,000 inches in a mile. If you scale the distance between our Earth and sun to the length of a single inch, then a light-year on this scale would equal one mile.
JB: Excluding our sun, the closest star is over 4 light years away. So if there’s one inch between the Earth and sun, it’s 4 miles, or 6 kilometers, between us and the nearest star.
DB: Special thanks to Research Corporation, a foundation for the advancement of science. We’re Block and Byrd for Earth and Sky.
What is a light year? from howstuffworks.com
Light year, from the Electronic Sky
