Wilhelm Schur

Wilhelm Schur was born on 15 April 1846 in Altona, Hamburg, to the wine merchant Friedrich Wilhelm Schur and his wife Johanna Tormählen.[2] Schur showed mathematical prowess early in his life, entering and winning a mathematics competition organised by the Educational Association of Schleswig-Holstein and Lauenburg at the age of 14.[3] As grandson of Adolph Cornelius Petersen (28 July 1804 – 3 February 1854), the director of the Altona Observatory, Schur took numerous opportunities to acquaint himself with astronomy. Following Petersen's death, he shadowed Heinrich Wilhelm Theodor Seeling,[lower-alpha 1] an astronomer at the observatory, and made numerous simple astronomical observations and calculations.

By 1864 Schur was attending a polytechnic in Hamburg. That summer, he enrolled at the University of Kiel, where he studied mathematics and astronomy under Georg Daniel Eduard Weyer, physics under Gustav Karsten, and philosophy under Friedrich Harms. In the winter semester of 1864/1865 he transferred to the University of Göttingen, where he studied mathematics under Moritz Stern and Karl Hattendorff, physics under Wilhelm Eduard Weber, and astronomy under Wilhelm Klinkerfues, whom Schur was particularly fond of.[3] In April 1867 he published his first astronomical paper, titled "Bahnbestimmung des Doppelsterns Σ 3062" ("Orbit determination of the double star Σ 3062"), in the Astronomische Nachrichten journal. In October of the same year he earned a PhD, under the advisory of Klinkerfues, with a thesis titled "Untersuchungen über die Bahn des Doppelsterns 70 p Ophiuchi" ("Studies on the orbit of the double star 70 p Ophiuchi").[5] In the winter of 1867/1868 Schur moved to the University of Berlin, where he attended lectures in astronomy by Arthur von Auwers and Wilhelm Foerster and in physics by Heinrich Wilhelm Dove, Johann Christian Poggendorff, and Georg Quincke.

While at the University of Berlin, Schur briefly worked with von Auwers on understanding observations made by English astronomer James Bradley.[1] From November 1868 until the end of 1872 he worked as an assistant at the Royal Prussian Geodetic Institute, doing triangulation work in central Germany. He, however, sought to participate in the observation of the transit of Venus in 1874 and resigned from his post in 1872 to seek any opportunities to fulfill his wishes. He temporarily worked at the Berlin Observatory before being hired as an assistant at the Strasbourg Observatory in July 1873. Under the observatory's director, Friedrich Winnecke, Schur assisted in preparatory work for the expedition and joined the crew when they embarked for Auckland Island in July 1874. They arrived at their observation site in mid-October and observed the transit on December 9th, collecting data and finalizing measurements before embarking for home in June 1875. The expedition lasted 111 days in total.[3]

Wilhelm Schur (second from the left, front row) with the 1874 Venus transit expedition crew to Auckland Island.

Upon his return, Schur continued his work at the observatory. He quickly climbed the ranks; he was promoted to an observer in 1877 and, when Winnecke fell ill in 1882, he took over direction of the observatory as deputy director. He oversaw the setup of astronomical instruments at the newly built observatory and made extensive observations and measurements using transit instruments and heliometers. In 1873 he made measurements of Jupiter's bands and in 1883 published "Bestimmung der Masse des Planeten Jupiter aus Heliometer-Beobachtungen der Abstände seiner Satelliten" ("Determination of the mass of the planet Jupiter from heliometer observations of its satellites").[3] His work throughout this period was mainly focused on the apparent magnitude of variable stars and on the determination of comet orbits.

Map of the Beehive Cluster created by Schur in 1894

On Easter 1886 Schur was appointed to the University of Göttingen as Professor of Practical Astronomy and Director of the Göttingen Observatory. Throughout 1887/1888 he led a complete redevelopment of the observatory in which "almost only the walls remained untouched." Major projects included the renewal of the main hall's roof and the replacement of the outdated dome with one manufactured by Grubb in Dublin, Ireland.[3] In contrast to his predecessor, Wilhelm Klinkerfues, Schur was very successful in modernizing the inadequate equipment of the observatory, acquiring a new, large Repsold heliometer in 1888. In the following years Schur devoted all of his time to working with the new instrument. Among his most important works was the triangulation of the Beehive Cluster in 1894 and the two star clusters h Persei and χ Persei, which together form the Double Cluster, between 1891 and 1896. Averaging the results of his Beehive Cluster measurements led to 123 equations with 74 unknowns, which he resolved according to Gauss' method of least squares. The calculations were a tremendous amount of work and thus required 10 weeks to complete.[3]

In addition to his own research, Schur took on a number of other projects, including administrative and historical tasks. Together with an assistant, he catalogued and organised over 11,000 books and brochures in the observatory's library over a period of a year and a half, finishing in 1899 and leaving the library "in an orderly condition for the first time in 44 years." In 1891 he published a star catalogue of 6000 astronomical objects, which his professor and fellow past director of the observatory Wilhelm Klinkerfues had observed from 1858 to 1869.[6] In 1899 he published another catalogue, this time of comets and minor planets observed by Wilhelm Olbers from 1795 to 1831. For the 150th anniversary of the Göttingen Academy of Sciences in 1901 he wrote a historical overview of the development of astronomy in the Kingdom of Hanover and neighbouring areas.

At the beginning of 1901 Schur began exhibiting symptoms of severe stomach cancer and his health began to rapidly deteriorate. He was left housebound and could only partially continue his work. He failed to recover and died in the evening hours of 1 July 1901.[3]

An extensive list of Schur's publications can be found on the Astrophysics Data System.

• Carl Friedrich Gauss, mathematician and physicist who held directorship of the Göttingen Observatory from 1807 to 1855.
• Hermann Krone, photographer who joined Schur on the expedition to observe the 1874 Venus transit.