Henrietta Swan Leavitt
By Tim Hunter
“Miss Leavitt inherited, in a somewhat chastened form, the stern virtues of her puritan ancestors. She took life seriously. Her sense of duty, justice, and loyalty was strong. For light amusements she appeared to care little. She was a devoted member of her intimate family circle, unselfishly considerate in her friendships, steadfastly loyal to her principles, and deeply conscientious and sincere in her attachment to her religion and church. She had the happy faculty of appreciating all that was worthy and lovable in others, and was possessed of a nature so full of sunshine that, to her, all of life became beautiful and full of meaning.” Written obituary of Henrietta Swan Leavitt by Solon Bailey as quoted by George Johnson in Miss Leavitt’s Stars.
"When the Smithsonian Institution’s Air and Space Museum opened in 1976, its first planetarium show concerned the universe-and credited Hubble with discovering the period-luminosity law for Cepheids. My letters to the directors of the museum and the Harvard College Observatory solicited some activity, but the conclusion was that the program taped by a famous movie star could not be corrected.” Vera Rubin (2005)
1. Introduction – Henrietta Leavitt and her legacy
Figure 1. Henrietta Leavitt. Credit AAVSO.
Henrietta Leavitt (1868-1921) was a quiet, hard working, modest individual who never sought fame or honors. She was burdened in her later life with considerable health problems and was deaf for a significant portion of her adult life. For nearly three decades she toiled away on the tedious task of measuring the brightness of star images on Harvard’s large collection of photographic plates, initially as an unpaid volunteer. Yet, by the end of her lifetime, Henrietta Leavitt had achieved world fame in astronomical circles even if it was far less than she deserved because of the poor treatment afforded women astronomers in the early 20th century. She was even nominated for a Nobel prize, and her legacy endures to this day (Johnson, 2005; Papacosta, 2004; Moore, 2002).
Leavitt published approximately 35 papers, several of which were printed posthumously. Table 1 summarizes her publications. All her papers detail her variable star work, and her posthumous publications were catalogs of data that she had worked on during her lifetime that had not been fully completed or had been overlooked for publication.
Leavitt discovered half the world’s known variable stars in her lifetime, and her discovery of the Cepheid period-luminosity relationship is one of the most important astronomical discoveries of the 20th century. Her Cepheid legacy remains with us today more than 100 years after its discovery. It is one of our most important tools for examining the Universe. If one uses the NASA Astrophysics Data System (ADS) hosted by the Computation Facility at the Harvard-Smithsonian Center for Astrophysics to search for references having the word “Cepheid” in their abstract for the period January 1, 2005 through August 31, 2005, 1026 selections are found. This truly reflects the importance of Cepheid variable stars.
2. Henrietta Leavitt’ early life and education
Henrietta Leavitt was born July 4th 1868 in Lancaster, MA, into a family with ties to early Puritan ancestors and with ties to four centuries of Leavitts in Yorkshire, England. In the 1880’s her father was the pastor at the Pilgrim Congregational Church in Cambridge, MA. Her mother’s name was also Henrietta Swan, and she was named for her mother. Henrietta was the eldest of seven children of the Reverend George Roswell Leavitt and Henrietta Swan [Kendrick] Leavitt. At least two of young Henrietta’s siblings would die at an early age (Johnson, 2005; PBS). The Leavitts were relatively affluent and well educated.
After the family moved to Cleveland in 1885, Henrietta enrolled in Oberlin college and completed two years of an undergraduate education there. She returned to Cambridge in 1888 and enrolled at the Society for Collegiate Instruction of Women (later Radcliffe College) and graduated in 1892 at the age of 24. Her degree was a certificate that stated if she were a man she would have been awarded a bachelor of arts degree from Harvard. Leavitt did not concentrate on science, but her courses included natural history and analytic geometry and differential calculus. In her senior year she also took a course in astronomy at Observatory Hill which is just up Garden Street from Radcliffe (Johnson, 2005; PBS). For the next two years she earned graduate credits in astronomy and worked for free at the Harvard College Observatory.
3. Leavitt’s Harvard career and life
3a. Edward Pickering and his philanthropists
In the late 1870’s under the direction of Edward C. Pickering (1846-1919), the Harvard College Observatory embarked on a survey to photograph and catalog the brightness and spectrum of every star in the sky accessible by the photographic means then available. Pickering, a brilliant physicist, became the director of the Harvard College Observatory in 1879 at the age of 32. He would remain its director until his death in 1919. Pickering was always short of funds and was adept at raising money from private philanthropists including Mrs. Henry Draper, William Boyden, and Catherine Bruce.
Figure 2. Edward Pickering. From: http://www.klima-luft.de/steinicke/ngcic/persons/pickering.htm
Henry Draper (1837-1882), a distinguished American amateur scientist and an early pioneer of astronomical photography, was a physician by trade and born into a prominent family. His father John William Draper (1811-1882) was also an accomplished doctor, chemist, and a professor at New York University (NYU). William Draper took the first daguerreotype of the Moon in 1839, and Henry Draper became a professor and dean of medicine at NYU. During his lifetime, Henry Draper received numerous awards for his accomplishments, including a Congressional medal for directing the US expedition to photograph the 1874 transit of Venus. His wife, Anna Mary Palmer (1839-1914), was a wealthy socialite prior to marrying Henry. Henry died prematurely from pneumonia after a hunting trip to the Rocky Mountains, and his wife established the Henry Draper Memorial in 1886 to support photographic research in astronomy. This Memorial funded the Henry Draper Catalog[ue]1 , a massive photographic stellar spectrum survey, and the Henry Draper Medal2 both of which are still important today (Gibson, 2001). The Henry Draper Catalog became one of the main research goals for the Harvard College Observatory for almost 40 years.
Uriah A. Boyden (1804-1879) a wealthy Boston inventor left $250,000 to a suitable astronomical institution to build an observatory on a mountain with better conditions than those currently available at the time of his death. In 1887, Pickering convinced the trustees of Boyden’s will to award this money to the Harvard College Observatory. This money was eventually used to establish the Boyden Station in the southern hemisphere. The southern skies were an important part of Pickering’s effort to complete a photographic survey of the entire sky.
Solon I. Bailey (1854-1931) (best known for his discovery of RR Lyrae variable stars and for his later history of the Harvard College Observatory) was sent to Peru to establish the Boyden Station. After much initial frustration and effort, Bailey finally settled on a site in the remote town of Arequipa in 1891. After a disastrous 2 years of mismanagement of the Arequipa station by William Henry Pickering (1858-1938), the brother of Edward Pickering, Bailey returned to Peru in 1893 with his family and started what was to become a significant photographic survey spanning many years. The Arequipa station was not closed by Harvard until 1927 when it was moved to South Africa to establish the Boyden Observatory (Fernie, 2001; Wikipedia).
Figure 3. Solon Bailey. From: http://www.klima-luft.de/steinicke/ngcic/persons/bailey.htm
Catherine Wolfe Bruce (1816-1900)3, a noted patroness of astronomy, gave donations to Harvard College Observatory and to the University of Chicago for the building of research telescopes, one of which is the famous Bruce Telescope at Yerkes Observatory. E.E. Barnard (1857-1923) used this telescope to produce his celebrated An Atlas of Selected Regions of the Milky Way published in 1927. Another famous Bruce Telescope is the 24-inch (61 cm) f/5.6 astrograph used by Bailey at Arequipa. Edward Pickering convinced Bruce to donate money for its construction.
This Bruce Telescope was the largest wide-field photographic reflector ever used, and it now resides at the Boyden Observatory in South Africa. Its objective was optimized for work in the blue photographic bandpass, and its 14 x17-inch plates recorded a sky area of 5.9 x 7.1 degrees with a plate scale of 60 arcseconds/mm. “The Bruce Telescope was used to systematically photograph the southern celestial hemisphere in the interval 1898-1904. At that time, one-hour exposures reached 14th magnitude and exposures up to six hours reached 18th magnitude. It required 1,008 plate centers to cover the entire celestial hemisphere, and 950 of these Bruce Regions were successfully photographed…” (Williams, 2000).
This treasure trove of plates from Arequipa combined with photographic plates from other sources provided the Harvard College Observatory with an increasing stack of data sources that had to be examined, measured, analyzed, and cataloged. By the 1890’s, the Harvard large scale photographic surveys had several thousand plates that needed to be examined. This required measuring stellar positions and stellar brightness and the tabulation of large amounts of data. Pickering was always full of ideas for projects and always short of the means to accomplish them. His goal of cataloging every star in the sky reachable required intensive use of skilled, but inexpensive labor. Pickering solved his problem by employing a group of women astronomers who each in her own way was creative, very well educated, and willing to work as a volunteer or for low wages. It is remarkable that Pickering was able to gather such a skilled group of assistants to work so hard and so brilliantly for so little remuneration or credit.
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The original Henry Draper Catalog was published by Annie Jump Cannon and EC Pickering between 1918 and 1924 as Volumes 91-99 of the Harvard Annals. It contains astrometric and spectroscopic data for 225, 300 stars down to 9th magnitude. It is variously referred to as a catalog or catalogue.
The Henry Draper Medal is awarded by the US National Academy of Sciences for contributions in astrophysics. Among notable award winners are EC Pickering (1888), William Huggins (1901), George Ellery Hale (1904), Henry Norris Russell (1922), Arthur Eddington (1924), Harlow Shapley (1926), Annie Jump Cannon (1931), and Subrahmanyan Chandrasekhar (1971).
The Astronomical Society of the Pacific (ASP) awards its highest honor, the Catherine Wolfe Bruce gold medal, for lifetime contributions to astronomy. Edward Pickering won the award in 1908, Edwin Hubble in 1938, and Harlow Shapley in 1939 (Tenn, 2003).