Summary

Black-Body spectra are continuous spectra emitted by dense objects.

• The hotter the object, the shorter the wavelength (the "bluer" it is).

Emission line spectra are only have a few lines produced by a low-density gas.

• Each spectrum is unique to the element emitting it, and is determined by the electron configuration in the element.

- Absorption Line spectra are produced by cold low-density gas in front of a hot black body.

• Looks like an emission line spectrum, but subtracted from a continuous spectrum.

- Reflection produces the colors we see not produced by "lights", determined by what colors are absorbed.

• If you turn out the lights and can't see it anymore, then it's not producing its own visible light - it's just reflecting (though it is producing its own infra-red light).