Thursday, September 24, 2015

Charlotte Moore Sitterly - Astrophysicist

Charlotte Moore Sitterly (September 24, 1898 – March 3, 1990)

This humble daughter of Quaker teachers went on to become one of the most important researchers in astronomy, with her works continuing to benefit science even now.

As a student at Swathmore College, she took a wide range of classes to expose herself to as much knowledge as possible. When it came time to pick a major, though, she went with the department in which she'd taken the most classes, which was Mathematics. And it's lucky for us that she did.

Upon graduation, her adviser recommended she apply to become a "mathematics computer" for astronomer Henry Norris Russell at the Princeton University Observatory. Whether her adviser knew how perfect a match this was or not is unknown, but history has proven that it was. She had only taken an introductory course in astronomy at Swathmore, but she was able to get up to speed very quickly working with Dr. Russell, a fast-thinking astrophysicist. Initially, her job was to carry out the mathematical calculations needed for his research, but soon she was also using the equipment to make readings.

Over time, she became much more than his "computer," she was his partner in astrophysics research. Together, they used spectroscopy to study the wavelengths of light and radiation emitted from stars. She became well known for her meticulous research and stubbornly detailed computations, and when Dr. Russell took a leave of absence, she decided to complete her Ph.D. in astronomy at the University of California at Berkeley.

While in California, she was sent to work at the Mount Wilson Observatory, where she studied the spectral lines emitted by the Sun to determine its chemical makeup. In fact, it was her research pictures from this work that helped to set the new International Angstrom scale, which was a commonly used unit of measurement for atomic-scale structures at the time.

After receiving her Ph.D., she returned to Dr. Russell's lab at Princeton, where she continued her research into spectral waves for several years before taking a break and joining the National Bureau of Standards. The reason for the move was two-fold: she wanted to help them create a document listing spectral measurements, and she wanted to be close to her husband, fellow astronomer Bancroft W. Sitterly's work in Washington, D. C. She did countless computations herself but also used her growing recognition within the scientific community to pull together data from others' research to expand her tables.

She is most well known for her compilation of this data into her epic A Multiplet Table of Astrophysical Interest -- intricately detailed tables listing atomic energy levels that continues to serve as a standard reference document around the world. When asked what she thought was her most significant contribution to sciences, she replied:
Oh, I don’t know. I think the 1945 Multiplet Table probably. It has had the most impact. All of the multiplet tables, and now my present series, I think, probably have had the most lasting influence on astrophysics and that has been my predominating interest. I have done those tables for the astronomers more than for the physicists. My greatest pleasure over the years has come from the research on the solar spectra. I am still deeply interested in the identification of solar lines as to their chemical origin.
One of her most important discoveries came when she detected technitium in the spectrum of sunlight. Prior to her research, technitium had only been found in particle accelerators, but never in nature.

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Read more about her life and work:

American Astronomical Society obituary

New York Times Obituary

Woman Astronomer's Blog

American Institute of Physics Oral History Project

Journal of Astronomical History and Heritage [PDF]

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