If a source produces light at a single wavelength, then its spectrum will appear as a single wavelength image of the slit.
Normally a spectrum is displayed with wavelength plotted along the horizontal axis, so this image would be a vertical line, so we call the image of the slit a spectral line.
The primary advantage is that diffraction gratings can be optimized for particularly high resolution, that is, with greater dispersion in wavelength.
The dispersing element spreads the light out into a multi-wavelength image of the slit.
Can you point me to some good articles on the topic, or perhaps cover some more advanced materials yourself?
The lightest elements (hydrogen, helium, deuterium, lithium) were produced in the Big Bang nucleosynthesis.
Astronomers have developed an elaborate, physically robust evolutionary theory to explain the abundances that we see throughout the universe.
While this theory may be explanatory, it has no predictive power.
If you go into technical details, then there are two processes of neutron capture called rapid process (r-process) and the slow process (s-process), and these lead to formation of different elements. Jagadheep is currently at the Indian Institute of Space Scence and Technology.
I discuss stellar spectroscopy and nucleosynthesis. Astronomers recognize two distinct episodes of nucleosynthesis, primordial (big bang), and stellar.