Re: [SG? No, OT!] Cammo

> you'll probably be
> spotted by your blackbody curve long before you could be spotted
> based on reflected visible light.

> Cure my ignorance. What is a blackbody emitter and blackbody curve?

Black is the best colour to absorb light. It absorbs light of all
colours
equally - ideally 100% of it. A black body is one that absorbs all
elements
of the electromagnetic spektrum, including infrared, ultraviolet,
microwaves
... In practice, no solid object is an ideal blackbody, because all
materials absorb unevenly. The closest we can get is a box, painted
black
inside, with a small hole. This hole is a pretty good blackbody.

So much for the intro, part 1.

Part 2.
Any object above absolute zero will radiate heat away. For room
temperature
objects, mostly in the infrared. Like absorbtion, the exact spektrum
depends
on the material. It now happens that a blackbody is also the perfect
heat
radiator in that it emits most efficiently and with the smoothest
spektrum.

If you heat the above mentioned box, the infrared - or even the visible
light if you bring it to a red heat - coming out of the hole is
blackbody
radiation.
The blackbody curve is the spektrum of that radiation - that is, how
much
infrared, red, yellow etc... light you get. The shape of it depends on
the
temperature, with the peak frequency rising with temperature. That's why
objects start in the infrared, then glow dark red (e.g.a kitchen stove
plate), then as they get hotter, bright red (an electris oven), yellow
(a
flame) or white (a lightbulb).

Oh, and the hotter the object, the more total energy is radiated.

Hope this helps
Karl Heinz