Richard Clark wrote:

Hi Richard,

The discussion of heat is more a metaphysical concept because it is
confused by our senses.

Entropy demands that everything inexorably cools by dissipating its
energy (heat) into the void of cold space. Hence, everything radiates
(and yet we spend very little time writing about it, except for Art).
A good deal of this entropic radiation is like waiting an infinite
time for a circuit with infinite-1 Q to stop ringing.

The sun burns bright in the cosmos, but the greater part of the cosmos
is unheated by the sun even though all of the cosmos is illuminated
(radiated) by the sun.

Direct observation 1: Put two plates out in the noon sun but
undisturbed by the motion of air. One plate of metal, the other of
glass. Which gets hotter? Same amount of radiation from a known heat
source, but clearly different results in heat. . .

This illustrates a classical confusion between heat and temperature,
probably aggravated by our use of "hot" as a description of temperature
rather than heat. Heat is energy. Absorption or transfer of heat results
in a change in temperature. "Hot" (high temperature) objects radiate
more heat than cold objects. The more heat an object, such as a plate,
absorbs, the higher its temperature. Once this basic distinction is
clear, a lot of the mystery disappears.

There are, of course, other mechanisms of heat transfer other than
radiation, namely convection and conduction. But heat transfer has the
same effect on temperature regardless of the mechanism.

When doing experiments with the sun's rays, you sometimes get
non-intuitive results, because there's a lot of energy (heat) at
wavelengths we can't see, particularly at the ultraviolet end. The
reflective or absorptive properties of an object aren't necessarily the
same at infrared or ultraviolet wavelengths as they are at visible
wavelengths. For an example, you can't see the difference in my skin
when coated with sun block or not. But there's sure a difference in
energy (heat) absorption!

Roy Lewallen, W7EL