Annie Jump Cannon
Annie Jump Cannon was an influential American astronomer born on December 11, 1863, in Dover, Delaware. She grew up in an environment that fostered her interest in astronomy, thanks in part to her mother's encouragement. Cannon graduated from Wellesley College, where she initially studied physics before returning to academia to pursue astronomy at Radcliffe College under Edward Charles Pickering. She became a key figure at the Harvard College Observatory, where she worked on the monumental task of classifying stars from photographic plates. Cannon developed the OBAFGKM classification system, which categorizes stars based on their temperatures, a method that remains in use today. Over her career, she classified nearly 400,000 stars and published the Henry Draper Catalogue. Despite facing challenges, including being partially deaf and restricted from using powerful telescopes, Cannon's work earned her numerous honors, including honorary degrees and recognition from international astronomical societies. Her legacy continues through annual awards recognizing outstanding women in astronomy and commemorative institutions named in her honor.
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Annie Jump Cannon
Astronomer
- Born: December 11, 1863
- Birthplace: Dover, Delaware
- Died: April 13, 1941
- Place of death: Cambridge, Massachusetts
American astronomer
Twentieth-century American astronomer Annie Jump Cannon created a system for stellar classification that was adopted by the International Astronomical Union. Cannon also catalogued nearly 400,000 stars. Her work, published as the Henry Draper Catalogue, became an important reference for astronomers.
Born: December 11, 1863; Dover, Delaware
Died: April 13, 1941; Cambridge, Massachusetts
Primary field: Astronomy
Specialty: Observational astronomy
Early Life
Annie Jump Cannon was born on December 11, 1863, in Dover, Delaware. She was the eldest of three children born to Wilson Cannon, a shipbuilder who also served as lieutenant governor of Delaware, and Mary Jump, a homemaker who shared her interest in astronomy with her daughter. The two would view the night sky from the roof of their house, taking notes by candlelight and comparing constellations with the help of a guidebook.
Cannon attended school at Wilmington Conference Academy (now Wesley College) in Dover. Her teachers, recognizing Cannon’s academic ability, recommended that she be sent to one of the newly established colleges for women. Cannon graduated as valedictorian of her high school class in 1880 and entered Wellesley College in Wellesley, Massachusetts, that fall. She studied with Sarah Whiting, a professor of physics and astronomy, who introduced Cannon to spectroscopy, the study of beams of light emitted by stars. They used a telescope fitted with a prism, called a spectroscope, which broke the beams into spectra, or patterns of colors and bands. This introduction to spectroscopy would prove useful later in Cannon’s career, but at the time, she had no plans to further her education or work in the sciences. Cannon graduated with a degree in physics—astronomy was not a major at the time—and returned home to Dover.
After Cannon’s mother died in 1893, Cannon decided to pursue a career in astronomy. She returned to Wellesley as a postgraduate physics assistant in 1894, but soon switched to Radcliffe College, the women’s college affiliated with Harvard University in Cambridge, Massachusetts. At Radcliffe, Cannon continued her studies in astronomy with professor Edward Charles Pickering, director of the Harvard College Observatory.
Life’s Work
In the late nineteenth century, the Harvard College Observatory had undertaken a massive project to photograph and classify all the stars in the sky. The project had been conceived by Henry Draper, a wealthy physician and amateur astronomer. When he died, his wife established the Henry Draper Memorial Fund to ensure that his vision would be carried out. The funds enabled Pickering to employ assistants. In 1896, he hired Cannon to join a team of women responsible for managing the photographic data obtained by the astronomers. There were piles of glass photographic plates, each with dozens of star images, that needed to be classified and indexed. The collection grew each night as astronomers added more plates.
Many of the photographic plates had been created using a spectroscope, which left a blurry image of a star. Cannon began to study the different patterns of spectra using a magnifying glass. She classified the stars based on a system that had been designed by Williamina Fleming, curator of astronomical photographs at the observatory, and Antonia Maury, another assistant. Fleming and Maury’s classification system used a series of letters from A to Q, with subdivisions. It was one of over a dozen systems being used at the turn of the century.
In 1911, Cannon succeeded Fleming and began to implement a new system of classification, based on Fleming’s work. Cannon selected the letters OBAFGKM to represent stellar temperatures in a range from the hottest to the coolest stars. “O” stars are the hottest, now known to be hotter than 30,000 kelvin, and emit blue rays; “M” stars are cooler than 4,000 kelvin, and emit red rays. Cannon coined the mnemonic phrase “Oh, Be A Fine Girl, Kiss Me,” to aid in remembering the order. The phrase became so popular that it has been included in many astronomy textbooks and continues to be taught.
Using the OBAFGKM method, Cannon classified every star that had been recorded at the observatory, down to the ninth magnitude—stars that can be viewed using 50-millimeter binoculars. The project involved over 225,000 stars. Her work was published in nine volumes between 1918 and 1924, as the Henry Draper Catalogue.
Much of Cannon’s work involved classifying stars in the Southern Hemisphere. In 1922, she spent a few months at Boyden Station, Harvard’s other observatory, located in the Peruvian Andes mountain range. That same year, her classification system was adopted by the International Astronomical Union. Cannon attended many of the union’s meetings across Europe. Although she was partially deaf, she never had a problem communicating with other astronomers or completing her work.
For her contributions to astronomy, Cannon received a number of honors. She was elected an honorary member of the Royal Astronomical Society of England in 1914, since women were not offered full membership at the time. In 1921, the University of Groningen in the Netherlands awarded Cannon an honorary doctorate in astronomy. She also received honorary degrees from Wellesley College and the University of Oxford in England in 1925—she was the first woman to receive this honor from Oxford. Cannon received other honors as well, including the Nova Medal of the American Association of Variable Star Observers in 1922 and the Draper Gold Medal from the National Academy of Sciences in 1931.
For the remainder of her career, Cannon continued to classify stars. She classified down to the eleventh magnitude, which are stars that appear fainter and can be viewed with amateur telescopes. Her work was published as the Henry Draper Extension in 1925 and 1949. Cannon also published catalogues of variable stars, including three hundred that she had discovered herself. She discovered five novae as well, stars that burn brilliantly and then gradually burn out.
In 1938, at the age of seventy-five, Cannon was appointed the William Cranch Bond Astronomer at the Harvard Observatory. She was the first woman to receive this appointment. Cannon retired in 1940 and died soon after, on April 13, 1941.
Impact
Over the course of Cannon’s career at the Harvard College Observatory, she classified nearly 400,000 stars. Cannon continuously improved upon, amended, and modernized Pickering’s original stellar classification system. In doing so, she expanded Harvard’s photographic catalogue of stars to approximately 200,000 plates. As a result, the Harvard Observatory gained international prominence for having the largest collection of stellar photographic plates in the world, and the Henry Draper Catalogue became an important reference tool for astronomers.
Despite the fact that Cannon rarely touched a telescope—women were not allowed to operate the more powerful telescopes during her time at Harvard—her contributions to astronomy were recognized nationally and internationally both during her lifetime and after. Most significantly, the OBAFGKM system she created for stellar spectra classification was adopted in 1922 by the International Astronomical Union as the official classification system for astronomers. Since then, astronomers have used Cannon’s classification system for their analyses of the stars, particularly in deciphering the relationship between their type and temperature.
The American Astronomical Society (AAS) honors Cannon each year by presenting the Annie Jump Cannon Award to a female astronomy student. Begun in 1934, the award was given by the American Association of University Women (AAUW) between 1974 and 2004. Wesley College named the Cannon Science Hall in her honor.
Bibliography
Cannon, Annie J., and Edward C. Pickering. Annals of the Astronomical Observatory of Harvard College: The Henry Draper Catalogue. Charleston, SC: BiblioBazaar, 2008. Print. A reprint of the Henry Draper Catalogue, pre-1923.
Kaler, James B. Extreme Stars:At the Edge of Creation. New York: Cambridge UP, 2001. Print. An overview of stellar evolution, explaining the natures of various star types. Stars categorized in groups such as brightest, youngest, and hottest. Includes the OBAFGKM mnemonic.
---. Stars and Their Spectra: An Introduction to the Spectral Sequence. 2nd ed. New York: Cambridge UP, 2011. Print. An overview of stellar spectroscopy. Covers the fundamental properties of stars and their spectra and provides the history of stellar classification.
Robinson, Keith. Spectroscopy: The Key to the Stars: Reading the Lines in Stellar Spectra. London: Springer, 2007. Print. A nontechnical guide to stellar spectroscopy, from the energy of an atom and what makes a spectral line through the radiation and magnetic fields of stars.