Astronomers use metric units, and in particular the cgs (centimeter-gram-second) system. The basic unit of distance is the centimeter (cm). There are 100 centimeters in a meter and 1000 meters in a kilometer.

What are the basic units of measure?

The SI base units and their physical quantities are the metre for measurement of length, the kilogram for mass, the second for time, the ampere for electric current, the kelvin for temperature, the candela for luminous intensity, and the mole for amount of substance.

## What are the units used to measure volume?

The U.S. Customary Units for measuring volume are ounces, cups, pints, quarts, and gallons. The Metric System units are milliliters and liters. When measuring a small liquid volume, such as a dosage of cough medicine, the best unit to use is milliliters or ounces.