Labels:text | paper | font | black and white | document OCR: SPECTROSCOPY MARKED a turning point in understanding the nature of stars. By classifying stars according to their spectral characteristics, astronomers came to understand how they are born, how they die, and the source of their energy. THE HARVARD SYSTEM The Harvard Observatory team began by classifying stars according to the strength of the hydrogen lines in their spectra. Stars with strong hydrogen lines were classed as type A; type B showed slightly weaker hydrogen lines, and so on. Later, team member Annie Jump Cannon (1863-1941) realized that hydrogen lines were strongest at a certain temperature, and that hotter and cooler stars had fewer hydrogen lines. She reordered the classification system according to temperature, and this system - O, B, A, F, G, K, M - is still used today. HERT ...
