“As far as I can tell, people arguing don’t really know what a “blackbody” is. Colose claims a blackbody is something with an emissivity of 1. I understand blackbody vs greybody applies to an ideal radiative spectrum which is a different concept from absorptivity/emissivity.
Can someone who knows please clarify?”
There are 3 ways to transfer energy: conduction, convection, and radiation.
In vacuum of space, radiation is how energy is transferred.
{Or no other way is considered significant or relevant.}
A blackbody would absorb all the radiation that hits it. So if blackbody was a meter square, and sunlight was 1000 watts per sq meter, a blackbody would absorb the 1000 watts of this energy. Once this blackbody were to reached a temperature it would emit 1000 watts per one square meter. At a temperature it absorbs and it emits all the energy. And it emits the energy in the spectrum of the Planck Curve- which varies depending on temperature of emitting body.
All matter emits and adsorbs radiation and max value of either is 1.
A blackbody has this maximum values of 1 for both emission and absorption. Since it absorbs all radiation, a blackbody doesn’t reflect any energy, it just absorbs and emits.
Or:
“black body, in physics, an ideal black substance that absorbs all and reflects none of the radiant energy falling on it. Lampblack, or powdered carbon, which reflects less than 2% of the radiation falling on it, approximates an ideal black body”
http://encyclopedia2.thefreedictionary.com/black+body
In contrast a greybody reflects and/or transmits some of the radiate energy.
It’s reflective and/or transparent to the radiation. Or loosely, not quite a blackbody
Or a bodyblack or greybody is nonexistance thing, but acts as absolute value- it’s a measuring stick.
Our sun, all stars, and planets roughly behave as blackbodies or can compared against a ideal blackbody.
Emission values of some materials:
http://www.omega.com/literature/transactions/volume1/emissivitya.html
Spacecraft designers design spacecraft of materials and structures which channel and moderate temperatures [due to heat created in the craft or radiation from exterior sources- the Sun and/or planetary bodies]