all stars are giant gas balls conducting nuclear fusion in their core, there
are different types of them, for which we observe a “signature” spectrum.
To study spectra, it is useful to keep the three Kirchhoff laws in mind:
1. A hot gas at high pressure has a continuous spectrum
2. A gas at low pressure and high temperature will produce emission lines
3. A gas at low pressure in front of a hot continuum causes absorption lines.