Line spectra are unique patterns of light emitted or absorbed by atoms, resembling discrete lines. These patterns serve as the "fingerprints" of different elements, providing critical insights into atomic structure and composition....

So we've made it all the way to the 20th century with the history of astronomy. Plenty had to happen to get us to that point, but the most amazing stuff is yet to come! Shortly after Einstein did his best work, a guy named Edwin Hubble...