1. Spectroscopy is used to analyze the spectrum of light from celestial objects. The spectrum acts as a fingerprint that reveals the atoms and molecules present. 2. There are three main types of spectra: continuum spectra which are continuous, and emission and absorption line spectra which feature lines at specific wavelengths. 3. By observing celestial spectra, astronomers can determine properties of stars, galaxies, and gas clouds like their chemical composition and velocity.