Karl Hermann Gustav Müller (7 May 1851–7 July 1925) was a German astronomer. He was born in Schweidnitz,

Silesia Silesia (, also , ) is a historical region of Central Europe that lies mostly within Poland, with small parts in the Czech Republic and Germany. Its area is approximately , and the population is estimated at around 8,000,000. Silesia is split ...

to a merchant father; his father died when Gustav was six. In 1870 he entered the

University of Leipzig Leipzig University (german: Universität Leipzig), in Leipzig in Saxony, Germany, is one of the world's oldest universities and the second-oldest university (by consecutive years of existence) in Germany. The university was founded on 2 Decemb ...

, then transferred to the

University of Berlin Humboldt-Universität zu Berlin (german: Humboldt-Universität zu Berlin, abbreviated HU Berlin) is a German public research university in the central borough of Mitte in Berlin. It was established by Frederick William III on the initiative ...

two years later. He was awarded a Ph.D. in 1877 with a thesis on the subject of

micrometer Micrometer can mean: * Micrometer (device), used for accurate measurements by means of a calibrated screw * American spelling of micrometre The micrometre ( international spelling as used by the International Bureau of Weights and Measures; ...

screws. Thereupon he became an assistant at the

Astrophysical Observatory of Potsdam Leibniz Institute for Astrophysics Potsdam (AIP) is a German research institute. It is the successor of the Berlin Observatory founded in 1700 and of the Astrophysical Observatory Potsdam (AOP) founded in 1874. The latter was the world's first o ...

. His primary career focus became the spectrum of the Sun and celestial photometry. Between 1880–82, he assisted

Hermann Carl Vogel Hermann Carl Vogel (; ; 3 April 1841 – 13 August 1907) was a German astrophysicist. He was born in Leipzig, Kingdom of Saxony. From 1882 to 1907 he was director of the Astrophysical Observatory, Potsdam. He made extensive discoveries ...

in building a catalog of

stellar spectra Astronomical spectroscopy is the study of astronomy using the techniques of spectroscopy to measure the spectrum of electromagnetic radiation, including visible light, ultraviolet, X-ray, infrared and radio waves that radiate from stars and othe ...

. In 1877 he began making photometric observations of the planets and their atmospheres. He led the German expedition to Hartford, Connecticut, to observe the

transit of Venus frameless, upright=0.5 A transit of Venus across the Sun takes place when the planet Venus passes directly between the Sun and a superior planet, becoming visible against (and hence obscuring a small portion of) the solar disk. During a tr ...

in 1882. In 1886, he began a collaboration with Paul Kempf to assemble the ''Potsdam Durchmusterung'', which was a stellar catalogue of all stars in the northern hemisphere with a magnitude of 7.5 or brighter. In 1897 he published the manual ''Die Photometrie der Gestirne'' (The Photometry of Stars). Between 1900 and 1915, he and Hartwig produced a three volume catalogue of 1,687

variable star A variable star is a star whose brightness as seen from Earth (its apparent magnitude) changes with time. This variation may be caused by a change in emitted light or by something partly blocking the light, so variable stars are classified as e ...

s. Between 1896 and 1924, he served as a secretary of the ''

Astronomische Gesellschaft __NOTOC__ The ''Astronomische Gesellschaft'' is an astronomical society established in 1863 in Heidelberg, the second oldest astronomical society after the Royal Astronomical Society. In 1882, the ''Astronomische Gesellschaft'' founded the Centra ...

''. In 1918 he was elected to the

Prussian Academy of Sciences The Royal Prussian Academy of Sciences (german: Königlich-Preußische Akademie der Wissenschaften) was an academy established in Berlin, Germany on 11 July 1700, four years after the Prussian Academy of Arts, or "Arts Academy," to which "Berlin ...

, and he would also become an associate of the

Royal Astronomical Society (Whatever shines should be observed) , predecessor = , successor = , formation = , founder = , extinction = , merger = , merged = , type = NG ...

in England. From 1917–1921 he was the director of the Astrophysical Observatory at Potsdam. Due to legal requirements, he retired in 1921 at the age of seventy. He was married three times and had seven children. One son was killed during

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...

and a second in the aftermath. His son Rolf became an astronomer at the Potsdam Observatory.

References

{{DEFAULTSORT:Muller, Gustav 1851 births 1925 deaths 19th-century German astronomers Humboldt University of Berlin alumni Leipzig University alumni People from Świdnica 20th-century German astronomers Members of the Royal Society of Sciences in Uppsala