Theodor Jacobsen: a century of stargazing

At 98, Theodor Jacobsen, the former head of UW’s astronomy department is ready to publish a book

When Theodor Jacobsen began teaching astronomy at the University of Washington in 1928, space exploration was still limited to telescopes on the ground; NASA didn’t even exist and Sputnik was just another Russian word.

Theodor Jacobsen

When he retired nearly three decades ago, he went to work on a project that took him even further back in time. He began compiling information about the methods of astronomers who lived two millennia ago.

He never intended to publish his work, but fate lent a hand when three professors—Paul Boynton, Donald Brownlee and Woodruff Sullivan—visited the department’s patriarch at his apartment in a Seattle retirement community. There, on a table near the baby grand piano that he still plays, they noticed the neatly stacked manuscript and were amazed and delighted by its contents.

“I looked through the material and I thought, ‘This is something that needs to be archived and made available to scholars who study ancient astronomical models,’” Boynton said.

What started as a quest for personal satisfaction, to broaden his own knowledge about the history of astronomical theory, resulted in a book, “Planetary Systems from the Ancient Greeks to Kepler,” published this month by the UW Press.

In the book, Jacobsen, 98, examines the studies of ancient Greek philosophers, including Pythagoras, Plato and Aristotle, as well as those of top astronomers from this millennium, such as Ptolemy, Nicolaus Copernicus and Johannes Kepler. What he found were models for planetary and stellar movement that, while accurately reflecting positions of celestial bodies, sometimes contained strange motions—loops and zigzags, for instance. But he was more interested in how mathematical formulas used to create the models evolved in the centuries before Newtonian mechanics definitively explained both how the planets move and why they move as they do. The 250-page monograph contains some 80 detailed drawings of orbits based on the mathematical models of various astronomers.

According to Jacobsen, his book contains the basic information every astronomer should know. “I just thought the natural background for any astronomer is the development of astronomy since it began,” he said during a recent interview in his North Seattle home. “I thought it was unfair to call yourself an astronomer unless you had at least this minimum background.”

In fact, Jacobsen believes that, in this age of specialization, many of those working at major observatories “are technical physicists, not astronomers,” because they don’t have a basic grounding in the history of the science.

His colleagues agree.

A core value of the work, Boynton said, is that it provides an understanding of the sometimes difficult mathematical techniques ancient astronomers used to explain the workings of the heavens. That is done through Jacobsen’s translation of the geometric models used long ago into modern mathematical language. He has distilled many of those complex ideas into a readily understandable form for those who don’t want to read the original works, which were written in Greek or Latin.

Jacobsen’s astronomy department supporters were able to raise money from university sources and tap a number of volunteers to prepare the manuscript for publication. No one expects it to become a bestseller. Rather, about 500 copies are being published, primarily for library archives around the world.

Jacobsen’s interest in astronomy started in 1908 when, at the age of 7, he received his first telescope as a gift from his parents. It consisted of a 2-inch lens inserted into a paper tube. Three years later, a metal telescope with a 3-inch lens that his father had bought on a trip to Germany replaced the paper model. His new device had been a “finder” scope for a large, narrow-field telescope—it was used to locate bodies that then could be viewed close-up with the bigger scope.

In 1914, on the cusp of World War I, Jacobsen’s parents moved him and his brother and three sisters from Denmark to San Jose, Calif. From their new home they could see the University of California’s Lick Observatory in the Diablo Range east of the city. He recalled making the drive to the observatory in a used Chandler automobile, and how impressed he was with the sheer size of the telescopes. “We would never think of seeing such big instruments at that time in Europe,” he said.Jacobsen graduated from Stanford University and became a Lick Observatory Fellow at UC Berkeley, remaining for two years after receiving his doctorate in 1926. It was at Lick that he began his lifelong astronomical specialty—taking spectroscopic measurements of the four brightest Cepheid variables, stars a few-hundred light years from Earth, all visible with the naked eye. The stars are called variables because their brightness and size periodically increase and ebb. By recording the stars’ light on spectroscopic plates and then making precise measurements of the wavelength colors, astronomers can tell much about the distance and chemical composition of these stars.

In 1928, Jacobsen came to the UW as an assistant professor of astronomy and mathematics. A decade later he became a full professor of astronomy and “executive officer” of the department. He kept an office in the observatory near the Burke Museum, though even then the observatory was primarily for student use and public demonstrations. The only observatory device that Jacobsen employed was a special-purpose telescope called a meridian instrument, which he used to determine the time from stellar observations for his course in practical astronomy.

He typically taught two courses per quarter, with anywhere from 20 to 45 students in each. “If there weren’t enough students for two courses, they gave me a section of trigonometry or elementary mathematics to teach,” he said.

Jacobsen remained the sole member of the department for 37 years, until 1965, when George Wallerstein and Paul Hodge arrived as astronomy professors and Wallerstein became department chairman. (There are now 30 active astronomy faculty and postdoctoral researchers.) In 1971, Jacobsen assumed emeritus status and began working seriously on setting down some of the basic history of astronomy.

Jacobsen and his book will be celebrated at a special astronomy department colloquium—“Theodor Jacobsen: Seventy Years of Astronomy at the University of Washington”—at 4 p.m. on Thursday, Oct. 7 in Room A102 of the Physics/Astronomy Building. The book is available at University Bookstore and profits will go to the Jacobsen Fund for undergraduate and graduate astronomy education.

Jacobsen said he didn’t write the book with the public in mind because his style doesn’t suit a general audience. Nevertheless, he is pleased.

“It’s always satisfying to have your work published,” he said. ¶

Vince Stricherz, News & Information