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Nobel Prize for a “Computer” named Henrietta Leavitt (1868–1921)

by Pangratios Papacosta

Pangratios Papacosta came to the US from Cyprus (via the University of London, England) and
teaches science at Columbia College, Chicago. The following is a commentary on the life of
Henrietta Leavitt.

January 2005

The purpose of this short paper is to summarize the contents of a poster paper given by the author at the 2004 AAS annual meeting in Denver. The first objective of that poster paper was to disclose the content of letters by Professor Mittag, of the Swedish Academy of Sciences, and by Dr. Harlow Shapley, the director of the Harvard College Observatory. To the knowledge of the author none of these letters were published before. The second objective of the poster paper was to suggest that the importance of Henrietta Leavitt’s discovery, the period-luminosity relation, has not been fully recognized by the public or fully appreciated by the astronomical community. Detailed description of the life and works of Henrietta Leavitt and the difficult conditions under which she, like most women of her time, had to work are topics of future publication.

It is amazing that less than a hundred years ago people believed that our universe was just the
Milky Way galaxy and that the spiral nebulae seen at its very edge were just disorganized leftover material.
In 1924, only four years after the Great Debate between Heber D. Curtis and Harlow Shapley on the
size of our galaxy and on the possibility of “island universes,” Edwin Hubble showed that one of those
spiral nebulae, Andromeda, was indeed a galaxy with billions of stars, not at the edge of our galaxy but
almost a million light years away. Hubble was meticulous and thorough in his work, but even with
such refined qualities, he would not have been able to make this discovery if not for two other significant
factors. First, he was fortunate to be operating the 100-inch Hooker telescope at Mount Wilson, for
many years the largest telescope in the world. With such a powerful telescope Hubble could distinguish
individual stars in the arms of those spiral nebulae, stars that could provide hints of their distance and hence
distance of the spiral nebulae. Some of these stars were Cepheids, variable stars whose period
or cycle of brightness he could measure. The second factor is that he had at his disposal a newly established
method that used Cepheids as standard candles and therefore could measure distances that were much larger than those allowed by existing methods. Henrietta Swan Leavitt, the head of photographic photometry at the Harvard College Observatory, proposed in 1912 that a relationship exists between the period and luminosity of Cepheids. She made her discovery from photographs of the Small Magellanic Clouds that she was working on under the directorship of Edward Pickering, under whose name her paper was published.(1)

Her assignment at the time was to catalogue stars, not to investigate them. She made this famous
and extremely valuable discovery on her own initiative. Although Ejnar Hertzsprung was the first
to realize the value of such a discovery and made a crude calibration, it was Shapley who, after a revised
calibration, used it to measure the distances of globular clusters. Hubble used Shapley’s method to
measure the distance of the Andromeda nebula, and also the distances of many other galaxies; this led to
his 1929 discovery of the relationship between galactic speed and distance, as expressed in the famous
Hubble law. In his 1936 book The Realm of the Nebulae, Hubble refers to the newly discovered
property of Cepheids in the Small Magellanic Clouds as “a new feature of extraordinary significance.”(2) Yet he remains lukewarm when he mentions Henrietta Leavitt in the next paragraph. He acknowledges the
use and calibration of her period-luminosity relation first by Hertzsprung and later by Shapley and ends
the “Period- Luminosity Relations to Cepheids” section in his book without ever mentioning that he, Hubble, had used Shapley’s technique. Instead he writes,

“Thus, whenever a Cepheid may be found, the period will indicate the absolute luminosity, and
the apparent faintness then measures the distance. It was by this method that the first
reliable distances of nebulae were determined.”

Hubble’s underwhelming acknowledgment of Henrietta Leavitt is an example of the ongoing denial
and lack of the professional and public recognition that Henrietta Leavitt suffers from, despite her landmark
discovery. With the exception of naming a moon crater after her, the profession of astronomy has not
done much to celebrate her work. No astronomy prize is named after her and the period-luminosity
relation has not been renamed as the H. Leavitt law. The vision of the cosmos was dramatically enhanced
thanks largely to her discovery, yet no space telescope bears the name Leavitt and no USA postage stamp
has been issued to honor her. It is only through such bold changes that the public at large and the
community of astronomy and cosmology will fully recognize the importance of her discovery and
celebrate a true heroine of the profession. Sporadic efforts to recognize her work have been made in the
past, and occasionally words were written to elevate the significance of her discovery. But such words
remain private, at times confidential and often ignored. Here are some examples of such words and efforts.

“Miss Leavitt’s work on the variable stars in the Magellanic Clouds, which led to the discovery
of the relation between period and apparent magnitude, has afforded us a very powerful
tool in measuring great stellar distances. To me personally it has also been of highest service, for
it was my privilege to interpret the observations of Miss Leavitt, place it on a basis of absolute
brightness, and extending it to the variables of the globular clusters, use it in my measures of
the Milky Way. Just recently in Hubble’s measures of the distances of the spiral nebulae,
he has been able to use the period-luminosity curve I founded on Miss Leavitt’s work. Much
of the time she was engaged at the Harvard Observatory, her efforts had to be devoted to
the heavy routine of establishing standard magnitudes upon which later we can base our
studies of the galactic system. If she had been free from those necessary chores, I feel sure that
Miss Leavitt’s scientific contributions would have been even more brilliant than they were.” (3)

These were the words of Harlow Shapley, the director of the Harvard Observatory in a March
1925 letter to Professor Mittag-Leffler, a member of the Swedish Academy of Sciences. Dr. Shapley was
responding to a letter that Professor Mittag wrote earlier to Henrietta Leavitt, who unfortunately died
of cancer in 1921. Professor Mittag’s letter, dated February 23, 1925, begins with the following sentence:

“Honoured Miss Leavitt,

What my friend and colleague Professor von Zeipel of Uppsala has told me about your
admirable discovery of the empirical law touching the connection between magnitude
and period-length for the S. Cephei-variables of the Little Magellan’s cloud, has impressed me so deeply that I feel seriously inclined to nominate you to the Nobel prize in physics for 1926, although I must confess that my knowledge of the matter is as yet rather incomplete.”(4)

Unfortunately, Nobel prizes are not awarded posthumously and we will never know whether
Henrietta Leavitt would have received one had she lived longer. Regardless, the thought of nominating
her, which interestingly came from people outside the USA, speaks highly of the importance of her
discovery. Admittedly the importance of her work was felt only after Hubble made his dramatic discoveries, and had she lived longer, perhaps American astronomers would have recognized her in more
appropriate ways, something that I sadly doubt. Astronomy, like any field, needs heroes and heroines
that can inspire others and bring the subject to the public. We need to re-examine Henrietta Leavitt’s
contribution to astronomy and consequently to cosmology, using modern and current lenses of
evaluation. Only then can we realize the full impact of her period-luminosity discovery. One such
appraisal came in the work of historian of science Stephen Brush. In a 1979 article titled “The rise of
astronomy in America,” (5) Brush lists the most important discoveries in astronomy from 1800 until 1950, as recognized in the works and references of other historians of science. For the period of 1900–1950
he lists ten major discoveries, of which the second is the period-luminosity relation with the names of
Leavitt, Hertzsprung and Shapley attached to it.

We can explain but not justify the double standard treatment that women scientists like Henrietta
Leavitt suffered under. Those were difficult times for women and it is no secret that women were not
treated as equal to men in every field, including the arts and sciences. In the case of astronomy many
women were employed and given the title of“computer”, because their job was to examine
thousands of photographic plates, identify and catalog stars according to their apparent brightness
and spectral characteristics. They earned much less than men and did not receive the recognition that
they deserved. In a recent article entitled “Gender and science: Women in American Astronomy,
1859–1940,”(6) authors J. Lankford and R.L. Slavings say, “Women measured plates and reduced data in
the great factory observatories, helping raise American astronomy to world-class status while they
themselves were relegated to second-class status.” The authors suggest that such treatment merely
mirrored the values in American culture and the rigid application of gender-specific roles. They quote
Maria Mitchell, America’s first woman astronomer, who on the subject of gender-specific roles pointed
out some of the advantages that women astronomers had, over their male co-workers: “The eye that
directs a needle in the delicate meshes of embroidery will equally well bisect a star with the spiderweb of a
micrometer.” “Routine observations…dull as they are, are less dull than the endless repetition of the
same pattern in crochet-work.”(6)

Henrietta’s own personality compounded the situation of her relevant obscurity. In contrast to the
prevailing antagonism and professional competition amongst male astronomers like Hubble and Shapley,
Henrietta Leavitt was a humble, quiet and shy person, not because of her deafness but because of
her personality and character. These were very much shaped by her upbringing, in a family that was proud
of its Puritan ancestry and with a father who was a clergyman of national prominence. Such personal
qualities were well described by Solon I. Bailey of the Harvard Observatory, in the obituary that he wrote
for Henrietta Leavitt: (7)

“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.”


(1) Harvard College Observatory, Circular 173, March 1912
(2) The Realm of the Nebulae, by Edwin Hubble, Yale University Press, 1936, pp 14–16
(3) Letter, Shapley to Mittag, Harvard Library Archives, UAV 630.22, Box 13
(4) Letter, Mittag to Leavitt, Harvard Library Archives, UAV 630.22, Box 9
(5) Stephen Brush, American Studies, Vol.20, 1979, pp 41–67
(6) John Lankford and Rickey L. Slavings, Physics Today, March 1990, pp 58–65
(7) Solon I. Bailey, Popular Astronomy, Vol.XXX, No. 4 April, 1922 pp. 197–199

I wish to express my gratitude to the following institutions for their support, assistance and for
materials provided towards the Henrietta Leavitt project:
Columbia College Chicago, Harvard Archives Library, Harvard Observatory
AAVSO (American Association of Variable Star Observers).

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