[gary]

Originally Posted by yinyang23

Hi, I only recently joined IceInSpace and this is my first post:

What is black body radiation?

Welcome to the Group. Good to see you are up at Coonabarabran, one of
our favorite observing locations.

The radiation of a body that results from its temperature is called thermal radiation.
All bodies emit and absorb such radiation from their surroundings.

Matter in a condensed state, that is a solid or liquid, emits a continuous spectrum
of radiation.

Consider heating up an iron bar in a furnace until it glows. Initially it will glow
red and eventually blue-white. As the temperature increases the rod not only emits
more thermal radiation but the frequency of that radiation is becoming higher.

There is one class of objects that have an unusual thermal spectra known
as "blackbodies". These bodies have surfaces which absorb all thermal radiation
that strikes them. They do not reflect light and are black.

All blackbodies at the same temperature emit thermal radiation with the same
spectrum, irrespective of their composition.

Of particular interest are blackbodies which have a cavity in them
which is exposed by a small hole. Thermal radiation can enter the
hole, reflect inside and eventually be absorbed. If the hole is small,
little of the radiation will be reflected back out. So called 'cavity radiation'
was a vital key in the development of Quantum Mechanics, largely thanks
to the work of Max Planck who formulated a new postulate that accounted
for the unusual characteristics of blackbody radiation that weren't readily
explained by earlier classical theories.

To delve further and to appreciate the details, one would need to
study Quantum Mechanics, which is a second year course at university
and not for the mathematically faint hearted.
For many would-be engineers and scientists, that course often sees them
leave to pursue other endeavors.

Blackbody concepts are also used by astronomers and climate change
scientists in a classical (non-Quantum sense) to study the warming of Earth,
so it is important to appreciate the context of your question.

The Cosmic Background Radiation, a remnant of the Big Bang, also
has blackbody characteristics.

Hope this small amount of insight helps but in a nutshell, a blackbody is
exactly as the name suggests but its significance is that it absorbs all
thermal radiation and emits radiation when hot with a specific characteristic
spectrum, irrespective of what the object is made of.

Best regards

Gary
Mt Kuring-Gai