Enjar Hertzsprung

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Richard Fuerst

Mr. Percival

DE Astronomy

2 March 2012

Ejnar Hertzsprung

            Born on October 8th, 1873, a young Dane would be lead away from the field of astronomy; ironically, he would become one of our greatest contributors to the study of stars, this astronomer was Ejnar Hertzsprung. Ejnar Hertzsprung's father, Severin Hertzsprung, had a graduate degree in astronomy but, for financial reasons, accepted a position in the Department of Finances; he advised his son against the financial insecurity of astronomy, therefore Ejnar opted for chemical engineering as a career path. After graduating from the Polytechnical Institute in Copenhagen in 1898 and spent several years as a chemist before he began to study photochemistry in Wilhelm Ostwald's laboratory. During this period he began talking with astronomer Karl Schwarzschild, and within a few years he joined Schwarzschild as senior staff astronomer at the observatory in Potsdam. By 1919 Hertzsprung was the associate director and associate professor of the University of Leiden, and in 1935 he became its director. Hertzsprung retired in 1944 and returned to Denmark, continuing his research until 1966. He died at 94, thirteen days after his birthday.

           

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            What made Ejnar Hertzsprung so important to astronomy? Two words: Hertzsprung-Russell diagram; Hertzsprung work with stars and luminosity yielded the means for determining stellar distances, galactic structures, and distances to other galactic systems. His unique background consisting of photometry and chemistry made him more qualified in the emerging field of spectrometry. Before Hertzsprung contributed to our understanding of the physical nature of stars, we only knew the radial velocities and the spectras of different stars. It was not until 1905 and 1907 that he showed the relationship between the sharp/deep features of absorption lines and a star's luminosity in his papers called Zur Strahlung der Sterne. We could now measure intrinsic brightness with stellar spectra! The Hertzsprung-Russell diagram relates the luminosity of stars with their temperature, so high temperature / luminosity stars occupy the top right and low temperature/ luminosity rest in the bottom left areas of the scatter plot. Most stars are main sequence stars and have a direct relationship between their temperature and absolute magnitude. There are some stars, which Hertzsprung alludes to in his papers, that do not necessary follow the temperature/luminosity relationship. For example, red giants are very luminous yet lack the higher temperatures of their blue giant counterparts. Hertzsprung research was the cornerstone of the later illustration that became the Hertzsprung-Russell diagram. One diagram he did create was one for the Pleiades star cluster in 1906; he also inferred that stars of the same cluster would be approximately the same distance away from Earth. He concluded that this distance was negligible! He also constructed a diagram for the Hyades using this principle. Hertzsprung came up with the method of obtaining distances for binary-star systems and different photographic methods to help gather data on stars. Altogether he made 36,000 estimates of the brightness of variable stars. Finally his determination of the distance to the Small

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Magellanic Cloud ,  the furthest distance determined for that time (10,000 parsecs), earned him the gold medal of the Royal Astronomy Society.