STEM is for Everyone: Annie Jump Cannon, Classifier of Stars

By Amy Cowen on November 20, 2020 4:00 PM

Annie Jump Cannon's work evaluating the brightness of stars led to the spectral classification system used by astronomers today.

Icons related to space science and astronomy to represent Annie Jump Cannon's career and work classifying stars

A Fascination with Stars

Born in 1863, Annie Jump Cannon was fortunate that her mother encouraged an interest in astronomy. Cannon learned the constellations as a child, and she and her mother observed the stars in the night sky from a lookout in their attic.

Cannon's early love of the sky led her to study physics at Wellesley College. There are conflicting stories about when she got scarlet fever and lost most of her hearing, but many accounts suggest this happened while she was in college. A few years after she graduated, she returned to Wellesley as an assistant and began taking graduate courses and studying at Radcliffe College. During this time, she began working for Edward Charles Pickering at Harvard Observatory.

Mapping the Night Sky

With the goal of mapping all the stars in the sky, Pickering was overseeing the creation of a massive catalog of stars, the Henry Draper Catalog. Pickering wanted the catalog to contain classification for all stars to the 9th magnitude (a measure of brightness). At the time, the spectrum of a star was classified manually and in real time using a telescope and a prism. The observer would draw the rainbow spectrum and the dark lines that appeared when the star's light passed through the prism. These lines indicate the composition of a star. This process was advanced in Pickering's observatory by the use of photographic plates, which allowed spectral lines to be recorded (in black and white) so that they could be classified after the fact. This was an early form of astrophotography.

The problem was that there was so much data and so many stars to classify. Pickering hired a group of women, sometimes now referred to as Pickering's Women or Harvard Computers, to classify and catalog star spectra. (If you are familiar with the story of Hidden Figures and NASA's use of women for data analysis, this story may sound similar.) Pickering's Women analyzed stellar spectra, classifying thousands and thousands of stars, but for this process to be effective, they needed a common system.

Cannon is credited with developing the Harvard Classification Scheme, a system that classifies a star based on its temperature and spectra. (Her work on this system continued and evolved the work of two other women who had worked for Pickering.) Cannon's system classifies spectra using the letters O, B, A, F, G, K, M, rankings that correspond to temperature (hot to cold). The hottest stars are classified as O. (Many students learn this system with the "Oh, Be A Fine Girl—Kiss Me!" mnemonic device.) After assigning the spectral type letter, Cannon's system assigns a sub-class using numbers from 0 to 9.

Note: the Morgan–Keenan (MK) system used by many astronomers today is a variation of Cannon's Harvard Classification Scheme. The MK system still uses the OBAFGKM letters and numeric sub-classes but adds a Roman numeral or Roman numeral-letter pair (like Ia) to represent luminosity. Our sun, for example, is classified as G2V.

A Legacy of Stars

Cannon was known for her speed at classifying the spectra of stars and reportedly classified more than 350,000 stars during her career. She also discovered more than 300 variable stars.

While not much is written about Cannon's deafness or the role it played in her work, her loss of hearing clearly did not dissuade her from studying physics and astronomy and pursuing her passion for stars.

Another famous female astronomer, Henrietta Swan Leavitt, also worked for Pickering. Like Cannon, Leavitt also lost her hearing through illness. Leavitt discovered more than 2,400 variable stars, and her research on Cepheid stars and the relationship between their variable period and their luminosity provided a foundation for further research on parallax and discoveries made by Edwin Hubble and other astronomers about the size of the universe.

Explore Space Science and Astronomy with Student Projects and Lessons

Students inspired by Annie Jump Cannon's story and interested in space science, stars, and astronomy may enjoy projects like these:

The Milky Way and Beyond: Globular Clusters: investigate what can be learned about a globular cluster's composition and age from its color.
Using a Digital Camera to Measure Skyglow: experiment with using a digital camera to measure skyglow and see how it varies in different locations.
Which Stars Can You Use for Navigation in Different Parts of the World?: experiment to find out which stars can be used to navigate in each hemisphere of the globe.
Finding the Center of the Milky Way Galaxy Using Globular Star Clusters: use astronomical data about globular clusters to locate the center of the galaxy.
Star light, Star bright: How Does Light Intensity Change with Distance?: create a model of starlight and explore the relationship between brightness and distance.
X-Ray Vision: Seeing Into Space: use data from NASA's Chandra X-ray Observatory telescope to explore the process of colorizing images of objects in space.

Note: for more resources related to space science, see the Space Exploration Science Projects cutting edge area.

Educators can teach about space science and astronomy with lesson plans like:

Related STEM Careers

The following career profiles help students learn more about careers related to astronomy and space science:

Learn More

Annie Jump Cannon (National Women's History Museum)
Annie Jump Cannon (Space.com)
Cannon, Annie Jump (Wohlbach Library)
Meet Annie Jump Cannon, who cataloged and ranked over 300,000 stars by their hotness
Harvard's 'Computers': The Women Who Measured the Stars
Spectral Classification of Stars

The STEM is for Everyone Series

For more information about this series of profiles of scientists with disabilities and to learn about other scientists and engineers, see the following posts:

This post is part of our STEM is for Everyone: Scientists with Disabilities series. This series is made possible by generous support from Mitsubishi Electric America Foundation, a non-profit foundation jointly funded by Mitsubishi Electric Corporation of Japan and its US affiliates, working to make changes for the better by empowering youth with disabilities to lead productive lives.

Astronomy icons adapted from icons by Freepik from www.flaticon.com.