Question

Are blackbodies black?

Answer 1

No........It does not always appear black. The name derives from the concept of a black-body as a theoretically ideal absorber of light (and other electromagnetic radiation). However, that also happens to make it a perfect emitter.

A ideal black-body at “room temperature” would indeed appear black, but if heated enough it would start to emit light. This is shown in graphs of “black-body radiation”. The point is that if a black-body is a perfect absorber of light, it’s also a perfect emitter of light, when hot enough.

Incidentally, at room temperature a black-body will be emitting infra-red radiation, but that’s invisible to our eyes without special detectors and so it appears black to us. A temperature of around 900 Kelvin is needed for a black-body to become visible to us by emitted radiation alone.