Annie Jump Cannon

1863-1941

American Astronomer

Annie Jump Cannon was the first astronomer to develop a simple spectral classification system. She classified 400,000 stars—more than anyone else had achieved previously—and discovered 300 variable stars, five novas, and a double star. Cannon was the most famous female astronomer of her lifetime and was called the "Census Taker of the Sky." Cannon's successes inspired other women to pursue astronomicalinvestigations, despite gender biases demonstrated by many male astronomers.

Born on December 11, 1863, in Dover, Delaware, Cannon was the daughter of Wilson Lee and Mary Elizabeth Cannon. Her father served in the state senate. Cannon's mother transformed their attic into an observatory for Cannon to stargaze. At Wellesley College, Cannon studied with astronomer Sarah F. Whiting (1846-1927), who taught her new research methods. After graduating in 1884, Cannon returned home, where she focused on social activities, and traveled, photographing a solar eclipse in Spain in 1892.

After her mother's sudden death, Cannon dealt with her grief by resuming her astronomical observations. She began postgraduate studies at Wellesley in 1894, assisting Whiting in the physics laboratory. Cannon also studied astronomy at Radcliffe College with Edward C. Pickering (1846-1919), director of the Harvard Observatory. He encouraged female astronomers and hired Cannon in 1896 for a position at the observatory. She examined photographic plates after her classes and observed with telescopes at night. Initially, Cannon classified 5,000 stars monthly; eventually, she was able to analyze 300 stars per hour.

Cannon's most significant achievement was improving the stellar classification system that astronomers used to survey the universe. Previous astronomers had realized that when starlight is photographed refracting through prisms, it creates a spectrum. Researchers studied spectral patterns to identify star characteristics. Early classification systems arranged spectra alphabetically from A to Q, based on composition, or by Roman numeral designations, used to indicate stars' temperatures. Pickering asked Cannon to develop a better method to record star information. She determined that the elements that compose stars create different radiant wavelengths, which form various colors in spectra. By 1901 Cannon had outlined ten star categories, based on color and brightness, that were designated by letters (O,B,A,F,G,K,M,R,N,S). The first three stars were hot white or bluish, F and G were yellow, K was orange, and the final four categories were cooler red stars. Arabic numerals were used to identify subdivisions. Cannon classified the few spectra that did not fit into this system as "peculiar" and described them in detail. The International Solar Union adopted Cannon's classification system for use in observatories worldwide. Astronomers flocked to Harvard to learn her methodology. Although other classification systems were later developed, Cannon's techniques formed their framework.

Cannon also photographed and described variable stars, compiling an extensive database for other astronomers. She served as curator of the Henry Draper Memorial Collection and, during this work, compiled more astronomical data than had any other individual. She made sure that both the northern and southern hemispheres had been completely photographed, insisting that even the faintest stars be included. Ten volumes and two supplementary editions of her work were ultimately issued, listing each star with a number and description, including its position in the sky, its brightness, its visual and photographic magnitudes, and comments on any peculiarities. Because Cannon was the sole classifier, her observations and information were consistent. This central repository helped transform astronomy from a hobby into a scientific profession with a theoretical basis.

In 1931 the National Academy of Science awarded Cannon the first Henry Draper Gold Medal given to a woman. She created the American Astronomical Society's Annie Jump Cannon Prize to fund female astronomers' research. Cannon was named Harvard's William Cranch Bond Astronomer in 1938 and given the rank of professor. She died in Cambridge, Massachusetts, on April 13, 1941. Rooms at the Harvard Observatory and the Delaware State Museum as well as a memorial volume of the Draper Catalogue were dedicated to Cannon.

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