Here's my current understanding:
Emission spectra shows the wavelengths that have been emitted by the surface, and is used for analysing hot gases; whereas Absorption spectra shows the wavelengths absorbed by a surface.
Therefore, if you were to compare both the emission and absorption spectrum of a surface, the black lines on the absorption spectrum would correspond to the coloured lines on the emission one?
Assuming that this is correct so far ...
Why are emission spectrum's used to measure hot gases, and absorption for cold surfaces?
What difference does it make?
One last thing:
Light is given off when an excited electron descends into an underlying shell - because the energy it loses is given off as a photon, correct? ... But, what does this have to do with the temperature of a surface? As in: why does hot gas emit light?
I never really thought of this in too much detail before, and the [incomplete] solution seemed simple—the energy used in some 'crazy' process is thermal.. but what actually happens?
Surely if the electrons are excited, then they would ascend into an outer shell... if this is the case, then I'm guessing that the photon is produced when the electron falls back down to it's original shell... but what causes the electron to fall? A star is constantly bloody hot, so what would cause the electrons to lose the energy and fall ?
(Hope I'm clear [enough]). :)