Elizabeth Cornwall Tilley: Pivotal research on the Serpentis 59 d star system
- Sep 29
- 3 min read
In the vast history of astronomy, some stories shine brightly, while others, like distant stars, fade from view. Today, let’s rediscover one of those stories: that of Dr. Elizabeth Cornwall Tilley, an astronomer whose meticulous work in the 1940s unraveled the secrets of the 59 d Serpentis star system that was far more complex than it appeared.
The Discovery: More Than Meets the Eye in 59 Serpentis
To the naked eye, the star 59 d Serpentis is just another single point of light in the constellation Serpens. But astronomers with telescopes knew it was a visual double. The real mystery, however, lay hidden in the light of the brighter of these two stars.
In 1938, Tilley’s doctoral advisor, Dean B. McLaughlin, along with French astronomer R. Tremblot, independently discovered that the star’s spectrum showed not one, but three distinct sets of lines—a tell-tale sign of a triple star system. This was a rare find, but the system's intricate dance was still a mystery. This is where Elizabeth Cornwall Tilley's doctoral work began.
Her thesis, "A Spectrographic Study of the Triple System in 59 d Serpentis," became the first definitive work to calculate the complex orbital mechanics of this star. Analyzing spectrograms from the University of Michigan, Mount Wilson, and Yerkes observatories, she pieced together the puzzle.
Respected by her Peers
Her discoveries, published in The Astrophysical Journal in 1943 and were the subject of the American Astronomical Society , revealed a stunning cosmic arrangement:
The system was a spectroscopic triple, containing a large, cool G-type giant star (like our sun, but much bigger) and a pair of hot, white A-type stars.
These two "white twins" were locked in a tight embrace, orbiting each other once every 1.85 days.
This binary pair, in turn, orbited the larger G-type giant every 386 days in a wide, eccentric loop.
Combined with its distant visual companion, the system she studied was not single, double, or even triple—it was a quadruple star system. Her work was so significant that it was presented at a meeting of the American Astronomical Society and featured in The New York Times, which noted it was the only known triple-spectrum system for which the details had been fully determined.
About Elizabeth Cornwall Tilley
Elizabeth Roberts Cornwall, born in New Haven, Connecticut, in 1914, was a standout scholar from the beginning. She attended Vassar College, where her academic excellence earned her a place in the prestigious Phi Beta Kappa honor society upon her graduation in 1935. Her passion for science led her to Wellesley College for a Master of Arts degree, which she completed in 1939.
She attended the University of Michigan, where she pursued a Ph.D. in astronomy. It was there, under the guidance of noted astronomer Dean Benjamin McLaughlin, that she would make her mark. The 1940s were a transformative time for women in science, and Tilley was among those pushing the boundaries. It was also a personally transformative time; in 1942, while deep in her graduate studies, she got engaged to Thomas Clark Tilley.
Legacy of Elizabeth Cornwall Tilley
After earning her Ph.D. from the University of Michigan in 1943, Dr. Tilley’s professional path becomes less clear. According to a 1954 National Register of Scientific and Technical Personnel, her professional status was listed as "retired" just over a decade after completing her seminal work. Her listed specialties were "Spectroscopy of Astronomical Sources" and "Physics of the Sun," showing her deep expertise in the field.
While she didn't go on to mentor students of her own, her contribution to astronomy remains solid and undeniable. Her 1943 paper is still cited as a key reference for understanding 59 Serpentis, and her calculations for the stars' radii and masses laid the groundwork for future studies.
