02-14-2017, 06:38 AM
(02-12-2017, 09:41 PM)Duffy Wrote: When we are in the shadow of the sun i.e. night, we can see infrared radiation with thermal imaging as heat, but the source of heat we can see depends on the wavelength it is being emitted at eg a hot rock in the desert after sunset (black body) or a human being (continuous). Is this a fair assumption of the infrared spectrum, or do you need to be polite again ?
Actually, both the rock and the human body would radiate infrared 'heat' in the same way. That the human body continuously generates heat is irrelevant. All that means is it doesn't cool off as a rock eventually would.
A black body is an ideal object that absorbs all radiation. Not real.
A black body radiator is an object that is in thermal equilibrium with it's surroundings. It radiates as much energy as it absorbs.
The temperature of an object dictates the frequencies of electromagnetic radiation the object will emit. It's not just infrared.
The Sun (and other stars) are black body radiators. Even the visible light they give off is black body radiation. Stars range in color from red to orange, yellow, white, and to blue as their temperature goes up. Very hot objects emit visible light.
On the other extreme, very cool objects might not even emit infrared. The universe itself has cooled to only 3 degrees kelvin and emits radiation in the microwave region. This is the cosmic microwave background.