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Theodore Siegumfeldt Jacobsen (1901–2003)

Published onDec 01, 2003
Theodore Siegumfeldt Jacobsen (1901–2003)

Theodor Jacobsen, oldest member of the American Astronomical Society, died in Seattle on 17 July 2003 at the age of 102. His astronomical career, which began in the 1920's, coincided with the rise of astronomy in the University of Washington from a one-man activity within mathematics to today's major astronomical department of more than 30 faculty and other research personnel.

Born on 6 February 1901 in Copenhagen, Denmark, he immigrated with his parents, brother and three sisters to the USA in 1917. Even while he was still in Denmark, his interest in astronomy was sparked at age 7 by a gift from his parents of a two-inch telescope. As early as 1921, in the midst of his undergraduate studies in chemistry at Stanford, he wrote to Director W. W. Campbell of Lick Observatory, inquiring how he should prepare for a career in astronomy and whether one could make a living at it. Campbell encouraged him to learn as much physics and mathematics as possible with the outcome that, on completion of his BA degree at Stanford, Jacobsen became a University of California Berkeley graduate student and was appointed a Lick Observatory fellow in the period 1923 to 1926. Following completion of his PhD thesis, entitled ``A Redetermination of the Radial Velocity Curves of Certain Cepheid Variable Stars" (LOB, 379, 1926), he was appointed as ``assistant" at Lick, a position roughly equivalent to that of ``instructor" in a modern University environment.

Inquiries concerning whether Lick could recommend ``a promising young man to take over teaching some astronomy and math" from then President Spencer of the University of Washington were received by Lick's acting director Robert Aitken in 1928. They were looking for a Berkeley PhD, said Spencer, and Aitken responded with an enthusiastic recommendation of Theodor Jacobsen, who then took up his duties in Seattle with the beginning of the fall term 1928. Jacobsen succeeded H. Zanstra (of Zanstra mechanism fame) in the Dept. of Mathematics, but it was not until 1948 that astronomy was split off from mathematics, at which time Jacobsen became chair and sole member of the new Astronomy Department. During the World War II years, he taught navigation to the recruits who moved on to become naval officers. In the postwar years, he taught elementary astronomy, as well as more advanced courses in practical astronomy, the kinds of subjects found in Smart's "Spherical Astronomy" text including celestial mechanics and observational work using the UW Observatory transit instrument. He chaired the Astronomy Department until 1965 when the Department began to undergo its modern expansion; he formally retired in 1971.

Jacobsen's post-thesis research continued to center on the determination of radial velocities of cepheids as well as binary stars and he maintained connections on a modest scale with the Dominion Astrophysical Observatory in Victoria, B.C. In this era of emphasis on galaxy evolution and cosmology, it is easy to forget that in the 1920s, there was still controversy over the nature of cepheids---were they pulsating stars or merely some form of odd binary? Jacobsen's extremely accurate radial velocity curves of these stars, when combined with then newly emerging accurate light curves, did much to bolster the pulsation hypothesis. According to astronomers currently working in the field, Jacobsen's 1926 velocity curves, obtained with the then state-of-the-art Mills spectrograph attached to the Lick 36-inch refractor, attained an impressive accuracy in the gamma velocities of these cepheids of about 100 m/s! His last paper on cepheid velocities was a joint publication in 1992, written when Jacobsen was more than 90 years old.

He also was a major contributor to the study of the ``level effect," a term applied to the fact that during the pulsation cycle, the radial velocity curves differ depending upon the spectral line formation depth within the cepheid atmospheres. The effect was recognized as a result of the passage of a running wave, again a manifestation of the pulsation phenomenon in cepheids.

Although the astronomy of stars was Jacobsen's main focus, he was a man of many interests. He had a love of the mountains, especially the nearby Cascade Range. He was especially fond of one-day hiking trips around and on the flanks of Mt Rainier, although he never attempted the strenuous climb to the summit. But some of the lesser summits of the Cascade range were among his trophies: Mt Hood in the late 40s, and Mt St. Helens in the 30s when because of its graceful symmetry, it was known as the ``Fujiyama of the West." He was also an accomplished pianist, his tastes running from Beethoven to the early romantics such as Schubert and Chopin. In many ways, his pianistic philosophy paralleled his personal attitudes about doing astronomy. For him, precision and clarity took precedence over lofty grand strategies. He was happy to make what he called modest additions to astronomical research, standing as it were, ``on the shoulders of others." Along with this, he would lament over, for example, how difficult it was to make the last movement of Beethoven's Op.27, No.2 clear---to make it effective, he would say, you have to pay attention to the details, just as doing good astronomy meant paying attention to the details.

Jacobsen married Evelyn Brandt a well-known Seattle piano teacher. They kept Welsh Corgi dogs, which they named for various famous astronomers. Theodor and Evelyn played together at facing grand pianos, sometimes works for duo piano, sometimes piano concertos with the orchestral part in piano transcription. All this came to an end in 1993 when Evelyn died after 40 years of marriage. They had no children.

Jacobsen remained interested in classical astronomy---that of the Greeks and Arabs---as a kind of hobby during his entire life. But it surprised some members of the UW astronomy faculty when they found, on visiting Jacobsen in his home in the mid-90s, an extensive manuscript that he had composed using modern mathematics to rederive the laws of planetary motions as conceived by the ancients using far more primitive means. With the help of these and other colleagues, he was able to publish, at the age of 98, a UW Press book entitled ``Planetary Systems from the Ancient Greeks to Kepler."

Photo courtesy of University of Washington

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