Astronomy Bio...Hermann Carl Vogel

Jay Bitterman

Hermann Carl Vogel was born in Leipzig on April 3, 1841. He attended a grammar school in Leipzig, where his father was the principal, up to the age of 18. He continued his education at the Polytechnical School in Dresden and returned to Leipzig in 1863 to study Natural Science at the University. He became second assistant at the University Observatory soon after starting his course of study. He displayed so much dexterity at operating instruments that the director of the Observatory, Karl Bruhns, asked him to join the Astronomische Gesellschaft's "zone project". This was only a part of a much larger program that intended to scan the northern skies and to establish the coordinates of all stars down to the ninth magnitude. Vogel's task was to observe all nebulae within a specific zone. This work was the basis of his inaugural dissertation.

In 1870, on recommendation of Karl Bruhns and Johann Karl Friedrich Zöllner, a Professor at Leipzig Observatory, Vogel was appointed to the Directorship of an Observatory at Bothkamp near Kiel. The amateur astronomer F.G. von Bulow owned it. He won a prize from the Royal Danish Academy of Sciences for his work on the spectra of planets while he was at the Bothkamp Observatory. Vogel was given complete scientific freedom at the Bothkamp Observatory. There he had excellent equipment and sole discretion in determining the Observatory's research program. His concerted attention focused on the spectroscopic properties of stars, planets, nebulae, the northern lights, comet III 1871, and the Sun. Using a reversible spectroscope, he attempted to determine the rotational period of the Sun and, following attempts made by Huggins in England in 1868, he also attempted spectroscopically to determine the radial velocity of fixed stars.

In 1874 he was approached to become an observer at the proposed Astrophysical Observatory at Potsdam, near Berlin. Having been appointed as an observer to the future Potsdam Observatory, Vogel became increasingly interested in spectrophotometry.

In 1876 he utilized this technique to study Nova Cygni. His results provided the first evidence that changes occur in the spectrum of a nova during its fading phase. He also began an extensive study of the solar spectrum, but more precise tables compiled by using diffraction gratings soon superceded the results of his painstaking measurements. Vogel now decided to specialize in spectroscopy, and in response to a proposal made by Angelo Secchi, he examined the spectra of some 4,000 stars. He originally intended to classify the stars according to their spectra, a method that he assumed, would reflect their stage of development. However, he was dissatisfied with his results and dropped this work to go after a problem that had intrigued him since his days at Bothkamp Observatory - measuring the Doppler shift in the spectral lines of stars to ascertain their velocity.

In 1879 the Potsdam Observatory was officially opened and in 1882 he was appointed the first Director of the Observatory, a position he held until his death on August 13, 1907.

Vogel used photography to record stellar spectra, which led to his most sensational discovery, spectroscopic binary stars. His success was based on a study of the periodic displacements of the spectral lines of the stars Algol and Spica. They were eclipsing binary stars whose components could not, at the time, be detected as separate entities by optical means. From his spectrographs, Vogel determined the dimensions of this double star system, the diameter of both components, the orbital velocity of Algol, the total mass of the system, and in 1889 he derived the distance of the two component stars from each other.

Vogel's work settled the controversy concerning the value of Doppler's theory for investigating motion in the Universe. His discovery of spectroscopic binary stars not only led to the realization that such systems are a relatively common feature of the Universe; it also played an important role in the discovery of interstellar calcium absorption lines.