Temperature
 

The temperature is generally higher in the summer than in the winter, for example. Temperature is a quantitative expression of the average kinetic energy contained in matter. This is the most familiar definition. In general, for any given substance, the higher the temperature, the faster the atoms and molecules dance around. Temperature can be expressed in another way. For example, to measure the temperatures of distant stars, planets, and nebulae in outer space, astronomers look at the way they emit electromagnetic (EM) energy in the form of visible light, infrared, ultraviolet, and even radio waves and x-rays. By examining the intensity of this radiation as a function of the wavelength, astronomers come up with a value for the spectral temperature of the distant matter or object.

When energy is allowed to flow from one substance into another in the form of heat, the temperatures try to equalize. Ultimately, if the energytransfer process is allowed to continue for a long enough time, the temperatures of the two objects will become the same, unless one of the substances is driven away (for example, steam boiling off of a kettle of water). The kinetic energy of everything in the entire universe is trying to level off to a state of equilibrium. It won’t succeed in your lifetime or mine or even during the lifetime of the Sun and solar system, but it will keep trying anyway, and gradually it is succeeding. This process is known as heat entropy.