Dunér, Nils Christoffer
Born Billeberga near Helsingborg, Sweden, 21 May 1839
By substantially upgrading the Lund and Upsalla observatories, Nils Dunér placed Swedish astronomy on a modern footing with new equipment, improved observing practices, and introduced astrophysical techniques. Dunér was the eldest son of Vicar Dr. Nils Dunér and his wife Petronella (néeSchlyter). Nils and his 18-month younger brother Gustav, who later became a physician, were raised in a well-educated family. They received their first lessons from their father, formerly a teacher at several schools in Schonen and principal at the high school in Billeberga. At the age of eight, Nils was able to read Latin texts and improved his knowledge of French later in school, learning so fast that he finished high school before reaching the age of 17.
As a student at the University of Lund, Dunér began studying mathematics and attended astronomy classes under professor John Mortimer Agardh. But it was Dr. Axel Möller, Agardh’s assistant, who led and supported Nils Dunér in his studies. Dunér was so successful as a student that he worked as an assistant, first at the small university observatory and then at the Institute of Physics. He also participated in Otto Martin Torell’s expeditions to Spitzbergen in 1861 and 1862 and the 1864 expedition led by Nils Adolf Erik Nordenskjöld that prepared the trigonometric survey of these islands.
In 1862, Dunér presented his doctoral thesis on the orbital elements of the minor planet (70) Panopaea. In the fall of the same year, he was promoted to assistant at the observatory. After Möller succeeded Agardh as professor and director of the observatory in 1864, Dunér was promoted to observer.
Dunér immediately acquired a new 4-in. Steinheil refractor for the observatory located atop the university library. Agardh had applied for some money to build a new observatory in the southern parts of Lund (today Svanegatan 9), which was approved in 1862. Möller, as Agardh’s successor, supervised the construction of the new observatory, which was completed in 1867 with the installation of a new refractor with a 9.6-in. lens made by Merz in Munich. Dunér used the latter instrument for positional observations of comets and minor planets as well as micrometric observations of double stars. His catalog of 432 double stars was published in 1876. In 1877, Möller acquired a meridian instrument and initiated positional observations for the zone between 35° and 40°. These observations, begun in 1878 by Dr. Anders Lindstedt who later left for the observatory at Dorpat, were completed in 1882 by Dunér and Dr. Folke Engstöm, but the reduction of the data took several years. The results were not published until 1900 as part of the Katalog der Astronomischen Gesellschaft[AGK1].
In parallel to the zonal observations, Dunér turned his interest to the new field of astrophysics, in particular to spectroscopy. After 1878, Dunér undertook a spectroscopic survey, searching for red and orange stars matching Angelo Secchi ’s class III stars (today’s M-stars). He discovered more than 100 new candidates for this class. The results were published in a catalog of 352 stellar spectra in 1884. George Hale and Ferdinand Ellerman later commented on the difficulty of the visual observations that Dunér completed successfully in the prephotographic era of spectroscopy.
Dunér’s interest in spectroscopic work did not fade, but the observatory’s instruments limited his work to the brighter stars. In 1886, he acquired a Rowland grating, which formed the basis for a new spectroscope built by the Jürgensen Company of Copenhagen, a firm that made instruments for scientific, military, and industrial use. With this instrument Dunér determined the rotational period at different solar latitudes by measuring the Doppler shift of lines in the solar spectrum. His work confirmed and refined the rotational periods that had earlier been determined from sunspot observations by Richard Carrington . Dunér’s work had the additional benefit, as Axel V. Nielsen observed, of quieting opposition to the reliability of Doppler effects as an astrophysical tool. In 1899, Dunér repeated several of these spectroscopic observations with a larger instrument in Uppsala, confirming, in particular, the solar rotation results first determined in Lund.
In 1888, Dunér was appointed professor of astronomy and director of the Uppsala Observatory. By 1893, he had acquired a new double refractor for Uppsala; the mechanics by Repsold were equipped with Steinheil objective lenses of 13 in. for the photographic objective and 14.2 in. for the visual objective. Unfortunately, both lenses were technically unsatisfactory, and although Steinheil undertook to correct the problems, the double refractor was not in full service observationally until September 1899. Probably due to his age and the loss of time with the refurbishment of the telescope, Dunér’s activity decreased, but he continued to use this instrument for his observations of the Sun, work on double stars, and, together with Östen Bergstrand , engage in photographic astrometry of the minor planet (433) Eros in a campaign to determine the solar parallax. One of Dunér’s important results from his tenure at Uppsala was his demonstration that observational anomalies associated with the eclipsing binary star Y Cygni could be accounted for by substituting elliptical orbits for circular orbits. Dunér proposed that the two mutually eclipsing stars were both revolving around a common center of gravity with a common line of apsides, rotating in the planes of the two orbits. On 1 April 1909, Nils Dunér retired from his post as director; his assistant for several years, Bergstrand, succeeded him.
Dunér was awarded four prizes by the Swedish Academy of Sciences, the Rumford medal by the Royal Society of London in 1892, and the Lalande Prize by the French Académie des sciences in 1887. In 1863, he was one of the founding members of the Astronomische Gesellschaft. In addition to his research work, Dunér was a member of the planning commission for the Carte du Cielproject, and also member of a Swedish committee for the trigonometric survey of Spitzbergen. Moreover, he was a bank director as well as a member of the town council in Uppsala.
During his long and fruitful life as an astronomer, Dunér never had observed a total eclipse of the Sun. In August 1914, he traveled to Norrland with a small instrument to observe the eclipse, but it was to be his last astronomical observation. Dunér moved to Stockholm, where it would be more convenient to discharge his duties to the local Free Masons assembly and avoid frequent travel. Unfortunately, he fell ill with pneumonia and died shortly after his arrival.
In 1874, Nils Dunér married Hilda Aurora Trägårdh, the daughter of Vicar Carl Trägårdh and his wife Henriette (néeNelander). They had four sons.
- Dunér, Nils Christoffer (1862). Beräkning af planeten Panopeas banelementer. Lund.Google Scholar
- — (1876). Mesures micrométriques d’etoiles double faites à l’Observatoire de Lund, suivies de notes sur leurs mouvements rélatifs. Lund.Google Scholar
- — (1884). Sur les étoiles à spectre de la troisième classe. Stockholm.Google Scholar
- Hasselberg, B. (1917). “Nekrolog Nils C. Dunér.” Vierteljahresschrift der Astronomischen Gesellschaft52: 2–31.Google Scholar
- Nielsen, Axel V. (1971). “Dunér, Nils Christofer.” In Dictionary of Scientific Biography, edited by Charles Coulston Gillispie. Vol. 4, pp. 250–251. New York: Charles Scribner’s Sons.Google Scholar