Cannon, Annie Jump (1863-1941)

Cannon, Annie Jump (1863-1941)

American astronomer

Annie Jump Cannon developed a stellar classification system that is considered by many astronomers to be the foundation of stellar spectroscopy . The science of stellar spectroscopy analyzes the photographic spectrum of a star. The spectrum, a series of colors that can range from violet to red depending on the star's temperature , is produced by using a telescope to collect a star's light and to pass it through a spectroscope. The same effect occurs when sunlight passes through raindrops to produce a rainbow . The spectroscope also produces a series of narrow dark lines within the spectrum known as spectral lines. These lines give further clues to a star's temperature as well as composition, motion, and other information. Because the position of the spectral lines on the spectrum may vary greatly from one star to another, scientists sometimes refer to this spectrographic data as the fingerprint of a star and consider this information crucial to all stellar theories.

In devising her classification system, Cannon recognized the atmospheric temperature of a star as the most important of the various factors that determine the intensity of a star's spectral lines. Her method classified stars from hottest to coolest using capital letters to designate each major type of star. The letters O, B, A, F, G, K, and M represent the seven major categories. Cannon identified further distinctions within a major category by placing a number from zero to nine after each letter. For example, the Sun is a G–2 star.

Born in Dover, Delaware, Annie Jump Cannon was encouraged by her mother in the study of astronomy from an early age. Later, under the tutelage of two American astronomers, Wellesley professor Sarah Frances Whiting (1846–1927) and the Harvard College Observatory director Edward C. Pickering (1846–1919), Cannon became an expert in the relatively new field of astronomical spectroscopy.

It was Pickering who hired Cannon, along with a number of other women astronomers, to collect and catalog spectrographic data about the stars. Before attempting this enormous project, the astronomers needed a system by which hundreds of thousands of stars could be easily classified. Prior to Cannon's arrival at Harvard two other American astronomers, Wilamina Fleming (1857–1911) and Antonia Maury (1866–1952), had joined Pickering in devising two different classification systems. However, Pickering deemed both systems to be too complex or theoretical. Cannon borrowed from these earlier attempts in developing her own unique system of classification. Using her system, Cannon and her colleagues were able to classify the spectrum of over 300,000 stars. This information was published in the Henry Draper Catalog (1918–1924) and its extension (1925–1936). The catalog is considered to be a standard for stellar spectroscopy.

Cannon's 43-year career did not go unrewarded. In addition to receiving credit for the Draper catalogs, she also received recognition for discovering over 300 variable stars (which she incorporated into a catalog) and five novae. Cannon was the first woman to receive a doctor of astronomy degree from Groningen University (1921) and an honorary doctorate from Oxford University (1925). She was also the first woman to hold an office in the American Astronomical Society and to receive the Draper Award from the National Academy of Sciences (1931).

Scientists have used the work of Cannon and her successors to derive such information about stars as their motion, composition, brightness, and temperature. In turn, this information has led to theories about stellar life cycles. Modern astronomers, equipped with superior spectroscopes and computers have improved upon Cannon's work and are now able to sort stars into several hundred spectrographic categories. Evolving theories based upon such data are the legacy of Annie Jump Cannon's pioneering work in astronomy.

See also Stellar life cycle