A THERMOMETER measures the air temperature. Most thermometers are closed glass tubes containing liquids such as alcohol or mercury. When air around the tube heats the liquid, the liquid expands and moves up the tube. A scale then shows what the actual temperature is.

A RAIN GAUGE measures the amount of rain that has fallen over a specific time period.

A WIND VANE is an instrument that determines the direction from which the wind is blowing.

WEATHER SATELLITES are used to photograph and track large-scale air movements. Then meteorologists compile and analyze the data with the help of computers.