Otto Wilhelm von Struvé (May 7, 1819 (Julian calendar: April 25) – April 14, 1905) was a Russian astronomer. In Russian, his name is normally given as Otto Vasil'evich Struvé. Together with his father, Friedrich Georg Wilhelm von Struvé, Otto Wilhelm von Struvé is considered a prominent 19th century astronomer who headed the Pulkovo Observatory between 1862 and 1889 and was a leading member of the Russian Academy of Sciences.
Struvé was born in 1819 in Dorpat (Tartu), then part of the Russian Empire, as the third son out of eighteen sons and daughters of Friedrich Georg Wilhelm von Struvé 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. Yet, 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 adopted Russian nationality.
During 1843 and 1844, Struvé 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, the longitude was measured starting not from the Tartu Observatory, but from the Pulkovo Observatory. Struvé dedicated himself for much of the year 1844 to studying the Sun. He deduced its apex coordinates and linear velocity as 7.3 km/s. Although it was significantly smaller than the correct value of 19.5 km/s measured in 1901, Struvé's result was correct in that the velocity of the Sun was smaller than that of stars.
Struvé continued his father's work in several directions. In particular, they compiled famous Pulkovo catalogues of stellar coordinates, including several thousands double stars observed with a 15-inch refractor. Between 1816 and 1852, the observatory completed the famous survey triangulation measurements of the angular arc (named Struvé 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, he came to a conclusion that solar corona and protuberances are physically connected with the Sun and are not an optical effect, as most astronomers believed. Later in 1860 he suggested a close connection between solar protuberances and flares. Struvé also observed satellites of Uranus (Ariel and Umbriel, in 1851) and of Neptune. He also 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 had supported and developed the ideas of William Herschel that stars are formed from the diffuse matter. In 1872, Struvé organized assistance with equipment to the newly opened observatory in Tashkent – a southern 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.
Around 1845, von Struvé's father withdrew from most management activities at the Pulkovo Observatory and focused on individual research. From then on, most of administrative duties fell on von Struvé, 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, the son's health deteriorated as well, to the point that neither he nor his physician hoped for recovery. However, instead of retiring, von Struvé spent a full winter on leave in Italy and managed to restore his health.
Struvé remained a top authority at the Russian Academy and his requests, e.g. regarding staff appointments were always granted. The first refusal, in 1887, disappointed Struvé so much that he applied for resignation and was stopped from that only by the Tsar Alexander III, who requested Struvé to keep 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. Struvé had only limited command of Russian, yet he used it whenever possible.
Otto was the first scientist of the Struvé 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 Struvé, two US astronomers, Simon Newcomb and Asaph Hall were appointed as Foreign Members of the Russian Academy of Sciences.
Struvé 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, Struvé married Emma Jankowsky (1839–1902) and had another daughter with her. Two of his younger sons, Hermann Struvé and Ludwig Struve, continued the traditions of the Struvé 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 Struvé 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.
Struvé 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. The asteroid 768 Struveana was named in honor of Otto Wilhelm, Friedrich Georg Wilhelm and Karl Hermann Struvé; and a lunar crater was named for another 3 astronomers of the Struvé family: Friedrich Georg Wilhelm, Otto Wilhelm and Otto. The Struvé Geodetic Arc was included to the World Heritage List in 2005.
Otto Wilhelm von Struvé was elected an Honourary Member of the Astronomical and Physical Society of Toronto on 1894-01-09. He wrote back: "Only yesterday, I received your communication that the Astronomical and Physical Society of Toronto will honour me by nomination as Honourary Member. Probably my answer will come too late for the annual meeting; however, I will not let pass a single day without expressing my thanks to the Society for the intended honour. In fact, I shall feel proud to be made an Honourary Member in company of those men you named in your letter. Though, at my age, I can hardly expect to make myself essentially useful to the aims of the Society, I shall certainly do it if an occasion presents itself, and with the greatest of pleasure. With respectful compliments and thanks to Mr. Carpmael, very truly yours." His name was left off the list of honorary members starting in 1899.