Spectroscopy is second to photography with regards to importance. It was the photography of spectra that birthed Astrophysics. The term spectra is defined as the entire electro-magnetic wavelength.
Spectroscopy began in 1666 when Sir Isaac Newton discovered that white light passing through a glass prism split the light into a rainbow. To confirm this, Newton passed the rainbow through another prism and it recombined into white light.
Spectroscopy took off in the 19th century when Joseph Fraunhofer took a spectra of the Sun and noticed dark lines in the spectra. In 1857, Gustav Kirchhoff and Robert Bunsen experimented with laboratory chemical spectra and determined that each chemical element has its own unique spectral signature - called spectral lines. Furthermore, Kirchhoff summarized the three important elements of spectra, called Kirchhoff's Laws.
Why comet observations ?
BRIXIIS astronomical Observatory:
Astronomical spectroscopy as a new and fascinating observational technic of stars and comets