Isobars and Isotherms

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Isobars are areas of equal pressure. A "bar" is equal to the air pressure found at sea-level. This pressure is 14.7 pounds per square inch. Air pressure on earth is measured in millibars.  In the picture above the circles on the left show 980 mb and 1000 mb. The area inside the 980 mb circle are areas that have all the same pressure and same applies to the 1000 mb circle. A barometer is the weather instrument used to measure pressure.

Isotherms are areas of equal temperature. On the picture above, the circles on the right show 20 C and 24 C. The area inside the circle of 20 C all have the same temperature of 20 C and the same applies for the area within the 24 C circle. Temperature is measure with a weather instrument called a thermometer.