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by Bob Everoski
Distances in astronomy
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By Bob Everoski
June 19, 2013 4:31 p.m.

When referring to distances in our solar system, the most commonly used units of measure are the statute mile, the kilometer, and the astronomical unit (A.U.)

The statute mile, or regular mile, is equivalent to 5,280 feet. A kilometer equals 1,000 meters. Ten kilometers equals about 6.2 miles. Therefore, 100 kilometers is about 62 miles, a thousand kilometers is approximately 620 miles, etc.

The average distance from the Earth to the Sun is 93 million miles. Written out it would be 93,000,000 miles. This is also known as one astronomical unit (A.U.). One A.U. also equals approximately 150,000,000 kilometers.

Measuring distances outside our solar system requires different units, otherwise the numbers would get extremely large. The speed of light is 186,282 miles per second. In the metric system this is equivalent to nearly 300,000,000 meters per second or 3 X10^8 meters per second. If you multiply 186,282 miles per second times the number of seconds there are in a year, you would get about 6 trillion miles or written out would be 6,000,000,000,000 miles.

The speed of light is incredibly fast! The distance around the Earth’s equator is about 24,900 miles. Therefore, if you could travel at the speed of light, you could circle around the Earth’s equator almost 7.5 times in one second.

The next nearest star outside of our Sun is the Alpha Centauri Star system. It is a multiple star system, and is 4.3 light years away. Therefore, even if you were to travel to Alpha Centauri at the speed of light, it would take 4.3 years to get there. There are very few stars in our galaxy, the Milky Way, that are less than 10 light years away.

An even larger unit of measure used in astronomy is a parsec. It is equal to 3.26 light years, or 19.56 trillion miles. A kiloparsec is 1,000 parsecs, and a megaparsec is a million parsecs. These are literally mind boggling distances.

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