This diagram shows the structure of the Sun's interior. Two major regions inside the Sun, the convective zone and the radiative zone, are named for the way heat travels through them.
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The scientific field of thermal physics is concerned with heat and temperature. When we delve into topics such as global warming, the structure
of Earth's solid and liquid cores, and the way in which energy flows from the
center of the Sun to its surface, we need an understanding of thermal physics.
Temperature is a familiar concept that is a cornerstone of thermal physics.
Three scales for measuring temperature are in common use: Fahrenheit, Celsius
(or Centigrade), and Kelvin. The temperature of a gas is actually a measure
of the average speed with which molecules or atoms are hurtling about. We infer
the temperatures of stars from their colors; hot stars are blue while cooler
ones are red.
In our everyday speech, heat and temperature are nearly synonymous. In the
language of thermal physics, the two terms have precise and quite different
meanings. Heat is essentially the amount of thermal energy stored within an
Heat can flow from one object to another, transferring energy in the process.
The flow of heat can melt ice or warm the surfaces of planets near a star. The Laws of Thermodynamics
describe the fundamental physics of heat and its flows.
Heat tends to flow from hot places to cold ones, and often drives the motions
of other materials. Convection and conduction are two common ways by which
heat can flow. Electromagnetic radiation, especially at infrared wavelengths,
can convey heat across a vacuum. We study heat flows to understand the diffusion
of gases, the circulation of ocean currents, the outflow of energy from the
Sun, and the workings of rocket motors.
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