There are two types of line spectrum discussed as under:
Emission spectra - These are created when a gas is energised by some means - heat, electricity or light and the gas emits only certain colours which absolutely identify the ion or atom.
An emission line spectrum is dark at most wavelengths, but certain specific wavelengths are bright.
Absorption Spectra
Absorption spectra - These occur when when a gas cloud intercepts the light from a hot body and scatters those same colours as above. As less light now goes straight ahead, these colours are darker than the background full spectrum.
An absorption line spectrum looks like a continuous spectrum with certain specific wavelengths missing. These dark lines are the absorption lines.
Most stars have absorption line spectra because their cores are much hotter and more compressed than their surface layers. The hot opaque core produces a continuous spectrum. When this light passes through the outer layers of the star, that are cooler than the core, absorption lines are produced.
Organization of Line Spectrum
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