Simply put, there are two ways to look at air temperature: On the micro-scale, it is the small scale measure of gas molecules’ average kinetic energy; on a larger scale, it is the action of the atmospheric gases as a whole. In physics, an entire branch is devoted to objects’ temperatures and the transfer of heat between objects of differing temperatures. Called thermodynamics, it is a study that entails a great deal of mathematical knowledge.

No matter what the type of temperature discussed, the most common apparatus for measurement is the thermometer. The most familiar thermometers are thin, long, closed glass tubes containing some type of liquid—most often alcohol or mercury. When the temperature increases—or the air around the tube heats up—it causes the liquid to expand, moving it up the tube. Air temperature measurements are most commonly read in Celsius or Fahrenheit (for more about Celsius and Fahrenheit, see “Mathematics throughout History”).