Friedrich Georg Wilhelm von Struve

Friedrich Georg Wilhelm von Struve (born April 15, 1793, Altona, Den. [now in Germany]—died Nov. 23, 1864, St. Petersburg, Russia) was one of the greatest 19th-century astronomers and the first in a line of four generations of distinguished astronomers, who founded the modern study of binary stars.

To avoid conscription by the Napoleonic armies, Struve left Germany in 1808 and went first to Denmark and then to Russia. In 1813 he became professor of astronomy and mathematics at the University of Dorpat (now Tartu, Estonia), and four years later he was appointed director of the Dorpat Observatory. In 1824 he obtained a refracting telescope with an aperture of 24 cm (9.6 inches), at that time the finest ever built, and used it in a binary-star survey of unprecedented scope. In his survey of 120,000 stars from the north celestial pole to 15° S declination, he measured 3,112 binaries, more than 75 percent of which were previously unknown. He published his findings in the catalog Stellarum Duplicium Mensurae Micrometricae (1837; “Micrometric Measurement of Double Stars”), one of the classics of binary-star astronomy.

In 1835, at the request of Tsar Nicholas I of Russia, Struve went to Pulkovo to supervise the construction of a new observatory. He became director of the Pulkovo Observatory in 1839 but continued his binary-star studies.

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It was in 1835 that Struve began efforts to measure the parallax of Vega, a star he had selected for its brightness and large proper motion, which suggested that it might be near Earth. Parallax is the apparent shift in position of a nearby star, such as Vega, with respect to more distant stars as Earth moves from one part of its orbit to another. Astronomers had known since the time of Copernicus that stellar parallax must exist and had been trying seriously to measure it since the 1670s, but the instruments and techniques had not been good enough to measure such small angular shifts. In 1837 Struve announced a parallax for Vega of one-eighth of a second of arc, which is close to the modern value. Later, after continued measurement, he increased his estimate, but not for the better. Much more accurate parallaxes for other stars were announced in quick succession by German astronomer Friedrich Wilhelm Bessel in 1838 and by Scottish astronomer Thomas Henderson in 1839.