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How Long Is a Light Year?

Background: Dr. Art's Guide to Science, pages 88-89.

Light travels at the speed of 300,000 kilometers per second. In one second it travels 300,000 km. So, the distance of a light second is 300,000 km. We multiply by 60 to calculate that a light minute is 18,000,000 km long. Without looking in the book, show how you would calculate how long a light year is, and do the calculation.

Now, you can check the book on page 88. If you have a copy from the first printing of the book, you will see that Dr. Art made a mistake. He wrote 9,500,000,000 instead of the correct answer 9,500,000,000,000. That was a thousand times too small.

People often have difficulty understanding that a light year is a measure of distance since the word year is a measure of time, not distance. You can practice using other units of distance that include a unit of time.

How far is the distance from one end of a big room to the other end in crawling seconds; crawling minutes; walking seconds; or running seconds?

You can make up other units of measurement to describe distances such as from your home to a friend's house, or to a relative in a different city or country.

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