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(MUSIC) 
JOAN CARTAN-HANSEN, HOST:

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SCIENTISTS HAVE SPECIAL TERMS 
FOR MEASURING VERY SMALL AND

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VERY BIG DISTANCES.

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A MICRON IS ONE MILLIONTH OF A 
METER.

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SOME BACTERIA ARE A FEW 
MICRONS ACROSS.

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A NANOMETER IS ONE BILLIONTH 
OF A METER.

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THE DNA INSIDE THE CELLS OF 
YOUR BODY ARE ABOUT TWO

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NANOMETERS ACROSS.

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A PICOMETER IS ONE TRILLIONTH 
OF A METER.

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A HYDROGEN ATOM IS ABOUT 25 
PICOMETERS ACROSS.

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IN SPACE, DISTANCES ARE SO 
VAST THAT WE MEASURE THEM IN

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ASTRONOMICAL UNITS AND LIGHT 
YEARS.

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ONE ASTRONOMICAL UNIT OR A-U 
EQUAL 93 MILLION MILES, THE

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DISTANCE FROM THE EARTH TO THE 
SUN.

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SO, MARS, FOR EXAMPLE IS 1 
POINT 5-2 ASTRONOMICAL UNITS

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FROM THE SUN.

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A LIGHT YEAR IS HOW FAR LIGHT 
TRAVELS IN ONE YEAR.

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A LIGHT YEAR IS 60 THOUSAND 
ASTRONOMICAL UNITS.

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THE SUN'S CLOSEST STAR IS 
ALPHA CENTAURI AND IT'S 4

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POINT 4 LIGHT YEARS AWAY.

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FOR MORE INFORMATION ABOUT 
MEASUREMENT, CHECK OUT THE

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SCIENCE TREK WEBSITE.

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YOU'LL FIND IT AT SCIENCE TREK 
DOT ORG.