Final years

After 1841, Struve saw his position at the forefront of astronomy increasingly eroded by progress around the world. In Ireland, William Parsons, third Earl of Rosse, constructed a reflecting or mirror-based telescope of 6 feet (72 inches) aperture. From 1845 until 1917, this remained the world's largest aperture telescope. Perhaps most galling for Struve, Harvard University in the United States ordered from Merz and Mahler a replica of Pulkovo's 15-inch great refractor. Pulkovo no longer boasted the world's best instruments.

Beginning in the mid-1800s, photography grew in importance as a way of gathering data in astronomy. In 1845, the French physicists Leon Foucault and Armand Fizeau showed off the first daguerrotype of the Sun, showing sunspots and other features of interest to astronomers and physicists. From then on, photography conferred important advantages to those astronomers who learned the new techniques.

Not only were techniques and instruments evolving; the important questions in astronomy were changing, too. Precise observations of stellar positions and planetary orbits no longer dominated the field by the latter part of Wilhelm's career, replaced to some extent by questions concerning the physical nature of the stars and planets, which could only be answered using the new science of analyzing light, spectroscopy. No doubt, Struve felt the sands shifting under him.

After he published Etudes d'Astronomie Stellaire, Struve's professional life became less active and he spent more time with his family. He prepared previous work for publication; Positiones Mediae, the positions of the double stars he had listed in Catalogus Novus, appeared in 1852, and thereafter he applied himself to the first volume of Arc du Meridien, his major work on the geodetic surveys he had carried out or supervised. His letters to friends and colleagues related the family chronicles — his older children's marriages, and the efforts he and the other adults in the family made, in the absence of a school at Pulkovo, to educate the younger children by his marriage to Johanna, along with Otto's children.

In 1858, Struve, who had already been ill with infected sores behind his ears, developed a serious infection from a swelling on his neck. As the illness progressed, he became feeble, and could not recall anything from the past 20 years. Otto wrote to the Astronomer Royal George Airy of the sad state his father's health:

''When I came to his bed one morning, he spoke with me as if I were a complete stranger. On my remarking, 'Father, don't you know me? I am Otto' he first looked at me fixedly, then drawing me to himself with the words, 'Otto, my old comrade, I did not know you, that is terrible!' he broke out into a stream of tears — an appearance that we had never before known in him. From this moment the memory for recent times began to come back, but remained very weak.''29

Over the next few years, Struve did recover enough physically to take a restful family holiday in warmer climes, but he never returned to work. Otto and a former colleague had to complete the Arc du Meridien for him. In 1864, at the age of 71, he died of pneumonia. He lies buried on the grounds of Pulkovo, amid a grove of birch trees that he planted himself.

Struve's son Otto Wilhelm Struve remained at the helm of Pulkovo another 27 years after Wilhelm's death. Thereafter the directorship of Pulkovo passed out of the Struve family, but the Struve astronomical dynasty and tradition of leading observatories continued. Otto's son Hermann eventually took Bessel's place at the Konigsberg Observatory, then was tapped to direct the observatory that Alexander von Humboldt had helped establish in Berlin. Hermann's son Georg became an astronomer, and, like his great-grandfather Wilhelm and grandfather Otto, enjoyed a reputation as an excellent observer. Georg had two sons, one of whom studied astronomy but did not make a career of it.

Another of Otto's sons, Ludwig, followed even more closely than his older brother Hermann in the Struve family footsteps. Ludwig studied at his grandfather's alma mater, the University of Dorpat, and spent some time there as a professional astronomer, before being appointed director of the observatory at the University of Kharkov.

Ludwig's son, named Otto, was destined to carry on the Struve tradition in the United States. In the 1920s, the second Otto Struve earned a PhD in astrophysics at the University of Chicago and assumed the directorship of Chicago's Yerkes Observatory. During his tenure at Chicago he negotiated an agreement that led to the founding of the McDonald Observatory in Texas. The 82-inch aperture telescope there, the Otto Struve telescope, is still used most clear nights.

Otto would certainly have made his great-grandfather Wilhelm proud. Like each of his astronomer forebears, he received a Gold Medal from the Royal Astronomical Society in London. He edited the Astrophysical Journal; presided over the American Astronomical Society; chaired the department of astronomy at the University of California, Berkeley, and directed its Leuschner Observatory; and directed the National Science Foundation's first national observatory, the National Radio Astronomy Observatory in Greenbank, West Virginia. The Struve astronomical dynasty came to an end when he died, married but childless, in 1963.

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