Then you’re gonna love this photo of Annie Jump Canon.
Working at Harvard in the late 1800’s and early 1900’s as a “Computer”, Annie Jump Cannon cataloged stars using their spectra from photographic plates, in an effort to understand the mysteries and peculiarities of stellar spectra.
This was hard, detailed, nuanced work. By 1889, three years into her work, she had classified over 1,000 stars. By 1913, she could classify 200 stars an hour. She could classify three stars a minute, just by sight. Using a magnifying glass, she could classify stars down to 9th magnitude, 16 times fainter than the human eye can see. And she did this all with exceptional accuracy.
Over the course of her career, she personally classified more than 350,000 stars, accounting for a mind-boggling 98% of all contemporary stellar spectra classifications, a feat that wouldn’t be bested until the 1990’s with automated digital sky surveys.
Cannon used these classifications to develop the Harvard spectral classification system (O–B–A–F–G–K–M), organizing stars by surface temperature and physical properties.
It is hard to overstate just how foundational her work was to modern astronomy and astrophysics. Her classifications have enabled more than a century of breakthroughs in stellar structure and evolution, including the understanding of how stars change over time and how temperature, luminosity, and composition are related. The system underpins the Hertzsprung–Russell (HR) diagram, one of the most important tools in astrophysics, and remains embedded in modern research, from stellar population studies to galaxy evolution.
The immense scale of her work was itself a massive contribution to astronomy. For comparison, before Cannon, star catalogs contained between 600 and 4,000 stars. Her work single-handedly proved that large-scale stellar classification was both feasible and scientifically valuable. She helped establish systematic star catalogs as a core method of modern astronomy and laid the groundwork for astrophysical research on stellar structure, evolution, and populations that continues today.
