Measurements in Astronomy

For really, really big and faraway things!!!

U.S. Customary (English Units)Units of Distance

• Inch – good for measuring little things, like a pencil (thumb)

• Foot – 12 inches – good for measuring things like a room or a car (human foot)

• Yard – 3 feet – good for measuring things like a swimming pool or a football field (nose to finger)

• Mile – 1760 yards or 5280 feet – good for measuring distances between cities (1000 paces of Roman Legion)

• We’re used to thinking in these measurements, but it’s much harder to do calculations between them. Who wants to divide by 12 or multiply by 1760? Not you, I bet! That’s why metric is awesome!!!

The Metric System

• Also called the International System of Measurement – Why? Because every other country in the world uses it!

• If you know the prefixes of metric words, you’ll know how to convert between different units.

Prefixes to know

• Centi = 100 (cents in a dollar, years in a century)• Milli = 1000 (years in a millenium)• Kilo = 1000 (but kilo is really big, and milli is really

small)• So…

– 1000 millimeters in a meter– 100 centimeters in a meter– 1000 meters in a kilometer

Metric System Chart

mnemonic Metric Conversion Scientific Notation

King Kilometer 1,000 m 10 3

Henry Hectometer 100 m 10 2

Dies Dekameter 10 m 10 1

While Standard (meter, liter, gram)

1 m 10 0

Drinking Decimeter .1 m 10 -1

Chocolate centimeter .01 m 10 -2

Milk millimeter .001 m 10 -3

FYI

• Prefixes in metric are not just used for distance (meters). They are also used for mass (grams) and volume (liters) too! Isn’t that easy?!?

Scientific Notation

• Helps scientists make really, really big and really, really small numbers easier to write.

• Who wants to write 1,700,000,000,000,000,000,000,000 when you can write 1.7 x 1024, or 0.0000000000000000000000000002 when you can write 2 x 10-28?

Skill Builder: Scientific Notation

• Follow the four steps in the skill builder to fill in the chart on page 1, then answer the questions under part 2.