## V1000

10-3

one-millionth

1/1,000,000

10-6

one-billionth

1/1,000,000,000

10-9

Astronomers measure factors such as size or distance using the metric system, a decimal system of weights and measures in which the kilogram (2.04 pounds), the meter (39.37 inches), and the liter (61.025 cubic inches) are the basic units of mass, length, and capacity, respectively. Names for the most common other units are formed by the addition of the following prefixes to these terms: kilo- (thousand), mega- (million), giga- (billion), centi- (1/ioo), milli- (1/iooo), and micro (7: ,ooo,ooo). So, for example, a kilometer is a thousand meters, while a millimeter is one-thousandth of a meter. Some astronomical measurements using the metric system are shown in Table 2-2.

Table 2-2: Distances

Units

Examples

1 centimeter (cm) = io mil

Thickness of pencil: 7 mm

limeters (mm) = o.394 inches

Diameter of golf ball: 4 cm

1 meter (m) = ioo cm =

1,ooo mm = 39.4 inches =

Football field: 90 m

1.o9 yards 