A barometer is a scientific instrument used to measure atmospheric pressure, also called barometric pressure.
The atmosphere is the layers of air wrapped around Earth.
That air has a weight and presses against everything it touches as gravity pulls it to Earth.
Barometers measure this pressure.
Atmospheric pressure is an indicator of weather. Changes in the atmosphere,
including changes in air pressure, affect the weather.
Meteorologists use barometers to predict short-term changes in the weather.
A rapid drop in atmospheric pressure means that a low-pressure system is arriving. Low pressure usually means it will be cloudy, rainy, or windy. Air moves away from areas of high pressure. High-pressure areas usually create cool, dry air and clear skies.
A barometer measures atmospheric pressure in units of measurement called atmospheres or bars. An atmosphere (atm) is a unit of measurement equal to the average air pressure at sea level at a temperature of 15 degrees Celsius (59 degrees Fahrenheit).
The number of atmospheres drops as altitude increases because the density of air is lower and exerts less pressure. As altitude decreases, the density of air increases, as does the number of atmospheres. Barometers have to be adjusted for changes in altitude in order to make accurate atmospheric pressure readings.
