Dunér, Nils Christofer
Dunér, Nils Christofer
(b. Billeberga, Sweden, 21 May 1839; d. Stockholm, Sweden, 10 November 1914)
Dunér studied astronomy at the University of Lund and obtained his doctor’s degree in 1862. From 1864 to 1888 he was senior astronomer at the Lund Observatory. In 1888 he was appointed professor of astronomy at Uppsala University and director of the observatory. He retired in 1909.
Dunér’s dissertation of 1862 deals with the determination of the orbit of the planetoid Panopea, which had been discovered the previous year. Swedish astronomy at that time was of necessity strictly non-observational, as the observatories were obsolete. During the next few years a new observatory was erected at Lund, and Dunér became an observing astronomer, “the strict empiricist,” who introduced the “new astronomy” to Sweden. His work covered measurement of visual double stars and discussion of their relative movements; description and measurement of the spectra of red stars (the Vogel spectral type III), of which he discovered more than 100; spectroscopic determination of the rotation of the sun (a spectroscope with the largest grating of the time had been constructed); and observation and reduction of the star positions of the Lund Zone (declination +35° to +40°) of the meridian circle survey until the declination –23° of the Astronomische Gesellschaft.
Having transferred to Uppsala Observatory, Dunér again had to wait for improved equipment, but he succeeded in developing an efficient observatory. He revived his measurements of solar rotation and obtained further evidence for the decrease in the velocity of rotation from the equator to the latitudes ±75° (the results of his Lund measurements had also contributed to the waning discussion of the reliability of the Doppler principle). He continued his observations of the red stars; about twenty years later Hale and Ellerman pointed out how Dunér’s results, obtained visually and with small and primitive instruments, were confirmed photographically. Also at Uppsala he found the solution to the special problems of the eclipsing binary Y Cygni, pointing out that this system consists of two similar suns moving around their common center of gravity in elliptic orbits, the common line of apsides of which simultaneously rotates in the plane of the orbits. After summing up these results in a few lines Dunér added modestly: “These investigations may well claim some interest.”
In 1887 Dunér went to Paris as a Swedish delegate to the meeting concerning the gigantic Carte photographique du ciel project, and he was a member of the commission appointed to plan and supervise its effectuation. His foresight is apparent in his suggestion to postpone the project for a quarter of a century, in view of the rapid development of instrumental and photographic facilities that was expected. But his observatory did participate in the photographic campaign of the years 1900–1901 to determine the solar parallax by means of observations of the planetoid Eros.
In 1861 and 1864 Dunér was a member of expeditions to the Spitsbergen Islands as geographer and physicist, and his experiences were later taken into account by a joint Swedish-Russian geodetic survey of these northern islands about 1900.
In characterizing Dunér’s qualities as a scientist, Ångström, in his obituary, praised his clear mind for inductive reasoning and his great experimental genius.
I. Original Works. A bibliography of Dunér’s published papers is in von Zeipel’s obituary. Dunér’s more important works are “Mesures micrométriques d’étoiles doubles, faites à l’Observatoire de Lund, suivies de notes sur leurs mouvements relatifs,” in Acta Universitatis lundensis, 12 , no. 2, pt. 1 (1876), 1–266; “Sur les étoiles à spectres de la troisième classe,” in Kungliga Svenska vetenskapsakademiens handlingar, 21 , pt. 2 (1884), 1–137; “Recherches sur la rotation du soleil,” in Nova acta Regiae Societatis scientiarum upsaliensis, 3rd ser., 14 , pt. 13 (1891), 1–78; “On the Spectra of Stars of Class III b,” in Astrophysical Journal, 9 (1899), 119–132; “Calculation of Elliptic Elements of the System of Y Cygni,” ibid., 11 (1900), 175–191; “Om den på fotografisk väg framställda stjernkatalogen,” in Öfversigt of Kungliga Vetenskapsakademiens förhandlingar (1900), 399–407; and “Über die Rotation der Sonne,” in Nova acta Regiae Societatis scientiarum upsaliensis, 4th ser., 1 , pt. 6 (1907), 1–64.
II. Secondary Literature. An article on Dunér by Ö. Bergstrand is in Svenskt biografiskt lexicon, XI (1945), 528–535. Obituaries are A. Ångström in Astrophysical Journal, 41 (1915), 81–85; Ö. Bergstrand in Astronomische Nachrichten, 199 (1914), 391–392; A. Fowler in Monthly Notices of the Royal Astronomical Society, 75 (1915), 256–258; B. Hasselberg in Vierteljahrsschrift der Astronomischen Gesellschaft, 52 (1917), 2–31; and H. von Zeipel in Kungliga Svenska vetenskapsakademiens Årsbok för År 1916 (Uppsala), 291–312.
Axel V. Nielsen