77-88 Spectroscopy is a very important tool for astronomy. The textbook goes into much greater detail about the physics of spectroscopy than we need.
Molecules have many more lines than atoms.
We have to rely on the information carried in the light that travels to us. Different chemicals are different combinations of atoms and molecules. Thermal spectra Sketch the spectrum from a regular light bulb where the light is emitted by running electricity through a small wire and heating the wire to temperatures of about 5700 Kelvin. Label the Wavelength axis with appropriate units. The fact that light can behave like a wave and like a particle is very exciting to a physicist - but to an astronomer it is just two ways of thinking about light.