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American Morning

Ask CNN: How Do Scientists Figure Out How Long a Light Year is?

Aired September 06, 2001 - 09:52   ET

THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.

THIS IS A RUSH TRANSCRIPT. THIS COPY MAY NOT BE IN ITS FINAL FORM AND MAY BE UPDATED.
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BEN FRASER, NORCROSS, GEORGIA: Hi, my name is Ben Fraser. I live in Norcross, Georgia.

I would like to know how scientists figure out how long a light year is.

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ANN KELLAN, CNN SCIENCE AND TECHNOLOGY CORRESPONDENT: A light year is actually the distance that light travels in a year. Scientists have been trying to measure light since the days of Galileo. But not until the turn of the 20th century was it possible, when Albert Michaelson was able to measure the speed of light between two mountain tops in California by flashing a beam of light from one and reflecting it back off the other, then timing how long the round- trip took.

He found that light travels over 185 thousand miles per second. And after multiplying, found that light travels over 6 trillion miles in one year. That's a large number. It would take you 32 thousand round-trips from the Earth to the Sun. Or you could walk around the earth about 250 million times to travel a light year. That's a lot of walking, so you better have some good shoes.

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