# Otto Wilhelm von Struve

Otto Wilhelm von Struve (May 7, 1819 (Julian calendar: April 25) – April 14, 1905) was a Russian astronomer of Baltic German origins. In Russian, his name is normally given as Otto Vasil'evich Struve (Отто Васильевич Струве). He headed the Pulkovo Observatory between 1862 and 1889 and was a leading member of the Russian Academy of Sciences.

## Early years

Struve was born in 1819 in Dorpat (Tartu), then Russian Empire, as the third son out of eighteen sons and daughters of Friedrich Georg Wilhelm von Struve and Emilie Wall (1796–1834). He graduated from a Dorpat gymnasium at the age of 15 and was one year too young by the university rules. Nevertheless, he was admitted to the Imperial University of Dorpat as a listener and completed the program by the age of 20. While studying, he was assisting his father at the Dorpat Observatory. In 1839, he graduated from the university and moved to the newly opened Pulkovo Observatory, where he was immediately appointed as assistant of the director (his father). For his initial observations, he was given the degree of Master of Astronomy by the University of St. Petersburg in 1841. In 1842, he visited Lipetsk for observations of the solar eclipse and in 1843 defended his PhD. In 1843 Otto formally became a Russian subject.

## Scientific work

During 1843 and 1844, Struve participated in longitude measurements between Altona, Greenwich and Pulkovo, which were based on large displacement of chronometers over the Earth surface. This newly developed method was adopted in Russia, and from 1844, longitude was measured starting from Pulkovo Observatory instead of Tartu Observatory.
Struve dedicated much of 1844 to studying the Sun. He deduced its apex coordinates and linear velocity as 7.3 km/s. Although this was significantly smaller than the accurate value of 19.5 km/s measured in 1901, Struve was correct in that the velocity of the Sun was smaller than that of stars.
In 1865 Struve discovered NGC 8, a double star in the constellation Pegasus, and the spiral galaxy NGC 9 in the constellation Andromeda. He explored the constellation of Cassiopeia, finding double stars. He labeled them with his initials in the Greek alphabet, OΣ in his first catalogue, and OΣΣ in his appendix.
Struve continued his father's work in several directions. In particular, they compiled catalogues of stellar coordinates, including several thousands double stars observed with a 15-inch refractor. Between 1816 and 1852, the observatory completed survey triangulation measurements of the angular arc (named Struve Geodetic Arc). The measurements extended through over 2,820 km, from Hammerfest in Norway to the Staraya Nekrasovka village by the Black Sea, and aimed to establish the exact size and shape of the Earth.
In 1851, while observing a solar eclipse, Struve concluded that the solar corona and protuberances are physically connected with the Sun rather than being simply an optical effect, as most astronomers then believed. Later in 1860 he suggested a close connection between solar protuberances and flares. he also observed satellites of Uranus (Ariel and Umbriel, in 1851) and of Neptune. He measured the rings of Saturn and discovered (in parallel with other researchers) the dark inner ring of Saturn. In 1861, in his report to the Academy of Sciences, he supported and developed the ideas of William Herschel that stars are formed from the diffuse matter. In 1872, he organized assistance with equipment to the newly opened observatory in Tashkent – a more southerly location offering clear skies for observations. In 1874, he prepared several expeditions to monitor the transit of Venus across the solar disk in eastern Asia, Caucasus, Persia and Egypt. In 1887, he sent several groups within Russia to observe the solar eclipse. In some of those expeditions, he took part personally. In 1885, a 30-inch refracting telescope was installed at Pulkovo, at the time the largest in the world (see great refractor).

## Administration

Around 1845, von Struve's father withdrew from most management activities at the Pulkovo Observatory and focused on individual research. From then on, most administrative duties fell on von Struve, especially in 1858 when his father was gravely ill. With his father's retirement in 1862, Otto officially became director and kept that position for 27 years until 1889. In the mid-1860s, his own health deteriorated as well, to the point that neither he nor his physician hoped for recovery. However, instead of retiring, von Struve spent a full winter on leave in Italy and managed to restore his health.
Struve remained a top authority at the Russian Academy and his instructions regarding staff appointments were generally followed without question. The first refusal, in 1887, disappointed Struve so much that he applied for resignation. However, Tsar Alexander III requested him to remain in his posts until the 50th anniversary of the Pulkovo Observatory in 1889.
For most of those years, the working language of the Pulkovo Observatory was German, as the staff members were largely foreigners. Struve had only limited command of Russian, although he used it whenever possible.

## Visit to the United States

Otto was the first scientist of the Struve family to visit United States (in 1879: New York, Chicago and San Francisco). The visit served several purposes, including ordering the Alvan Clark & Sons optics for the new 30-inch telescope in Pulkovo, and it was a part of long-term Russia-US astronomy partnership during the 19th century. Within that collaboration, many American astronomers stayed at Pulkovo for observations and exchanged data with Russian scientists by mail. By the initiative of Struve, two US astronomers, Simon Newcomb and Asaph Hall were appointed as Foreign Members of the Russian Academy of Sciences.

## Personal life and late years

Struve was married twice. His first wife was a daughter of German emigrants Emilie Dyrssen (1823–1868). They had four sons and two daughters who reached mature age. A few years after her death, Struve married Emma Jankowsky (1839–1902) and had another daughter with her. Two of his younger sons, Hermann Struve and Ludwig Struve, continued the traditions of the Struve family and became distinguished astronomers. Of the older sons, one served at the Ministry of Finances and another was geologist. After retirement in 1889, Otto Wilhelm Struve stayed mostly in St. Petersburg, summarizing his observations and keeping correspondence with colleagues. He occasionally visited Switzerland and Italy. During his 1895 trip to Germany, he fell ill to the point of abandoning any further travel. He stayed in Germany and died in 1905 in Karlsruhe.

## Awards and honors

Struve won the Gold Medal of the Royal Astronomical Society in 1850 for his work on "The Determination of the Constant of Precession with respect to the Proper Motion of the Solar System" published in 1840 . He was a member of the Royal Swedish Academy of Sciences. Between 1852 and 1889, he was also a member of the Russian Academy of Sciences and became an academician in 1856. In 1874 he became foreign member of the Royal Netherlands Academy of Arts and Sciences. The asteroid 768 Struveana was named in honor of Otto Wilhelm, Friedrich Georg Wilhelm and Karl Hermann Struve; and a lunar crater was named for another three astronomers of the Struve family: Friedrich Georg Wilhelm, Otto Wilhelm and Otto. The Struve Geodetic Arc was included in the World Heritage List in 2005.