Transcript: Astronomical spectroscopy began with Newton dispersing the Sun’s light with a prism. In 1817, Joseph Fraunhofer dispersed the Sun’s light with much higher resolution and saw the spectrum crossed by narrow, dark absorption features. These features exactly corresponded to the wavelengths of lines from hydrogen in the laboratory, showing that the Sun was made of hydrogen. Fraunhofer had an interesting personal history. He was an orphan and as a child was working as an indentured servant in a lab and workshop of a man in Germany. A gas explosion caused the death of his mentor and the destruction of the lab. Fraunhofer wandered from the rubble dazed and confused and with no job and no home. His story was played in the local papers, and he got a new mentor and a start in life and became one of the foremost astronomers of his time. In the 1870s, photography advanced to the point where people could make photographic spectra, and at that point stellar classification moved forward rapidly. In the modern age, Charge Coupled Devices or CCDs are used to record spectra of stars and other astronomical objects. These digital electronic detectors can produce high quality spectra of hundreds of thousands of objects, and so every spectrum is categorized by several types of features: the emission features and absorption features corresponding to the elements that make up the gas of a star and the continuum which peaks at a wavelength determining the temperature of the photosphere according to Wien’s Law.