On the night of August 14, 1879, in the small observatory building at the eastern edge of the city of Cordoba, Argentina, a thirty-seven-year-old woman named Petronila Astengo recorded the position of a southern star she had been observing on and off for three months. Her notebook gives the right ascension to within a few arc seconds of the value now accepted for the star designated HD 154760.
The notebook is held at the historical archive of the Observatorio Astronomico de Cordoba. It is one of forty-three notebooks she filled between 1873 and 1908.
Astengo was the first woman employed by the Argentine National Observatory. She held the position of calculadora, computer, from 1873 until her retirement in 1908. She performed the arithmetical reductions that converted raw observational readings into catalog entries. She also, by quiet expansion of her role over the years, did much of the observing.
The standard histories of nineteenth-century Argentine astronomy do not name her. The biography of the observatory's first director, Benjamin Gould, by the historian Lewis Boss, does not mention her. The official observatory history of 1971 does not mention her. The Argentine biographical dictionaries do not mention her.
She was recovered, in the historical sense, by the Argentine astronomer and science historian Beatriz Garcia, who in a 2003 paper for the Asociacion Argentina de Astronomia identified Astengo as the principal computer for the southern star catalogs published from Cordoba between 1879 and 1898.
Garcia's identification was based on the notebooks, which had been catalogued by the observatory in the 1980s without their authorship being widely noted, and on the surviving payroll records of the observatory.
The payroll records establish that Astengo was paid forty pesos a month from her hiring in October 1873, rising to ninety-five pesos a month at the time of her retirement. The male computers hired at the same period started at sixty pesos and rose to between one hundred fifty and two hundred. She did the same work for less money for thirty-five years.
She was born on April 19, 1842, in the city of Rosario, the second daughter of an Italian immigrant family. Her father, Tomaso Astengo, ran a small instrument shop on Calle Cordoba that sold surveying equipment, ships' compasses, and telescopes of modest quality. He had emigrated from Genoa in 1834.
Petronila received her early education at home and at the Escuela Normal in Rosario, from which she graduated in 1860 with what was then the highest level of mathematical preparation available to a woman in the city. She then worked as a teacher for ten years, primarily in Rosario but for three years in Buenos Aires.
She came to Cordoba in 1872 on the invitation of her uncle, a Jesuit astronomer named Father Vincenzo Astengo, who had been involved in early discussions of the founding of the national observatory. Her uncle introduced her to Benjamin Gould, the American astronomer hired by the Argentine government to direct the new observatory. Gould hired her the following year.
“She came to Cordoba in 1872 on the invitation of her uncle, a Jesuit astronomer named Father Vincenzo Astengo, who had been involved in early discussions of the founding of the national observatory.”
Gould's correspondence, held at the Houghton Library at Harvard, contains six letters between Gould and Petronila Astengo, all dating from the period 1879 to 1885. The letters are courteous, technical, and substantive. In one, dated March 4, 1882, Gould writes, your reduction of the proper motions of the catalog stars in the third quadrant is the most accurate I have received and I have therefore included it without revision.
Gould did not, however, include her name on any of the catalogs.
The first published southern star catalog from Cordoba, the Uranometria Argentina of 1879, lists Gould as author and acknowledges various assistants. The second, the Cordoba Durchmusterung, published in successive volumes between 1885 and 1894, lists Gould and three male astronomers. Astengo's name does not appear.
Garcia's 2003 paper traces her contribution to roughly forty percent of the calculations in the Durchmusterung, on the basis of handwriting analysis of the surviving working notebooks. The contribution includes the reduction of approximately 73,000 stellar positions.
Astengo also, in her own observational notebooks, recorded original observations of approximately seven hundred southern stars between 1879 and 1903. About two hundred of these observations were used in the published catalogs, again without attribution. The remaining five hundred remained in her notebooks.
Garcia, working with the historian Maria Cristina Pineda, has been able to identify twenty-three short papers in the Revista del Observatorio Astronomico and in the Boletin de la Academia Nacional de Ciencias between 1881 and 1905 that appear, on internal evidence and on handwriting comparison with surviving manuscripts, to have been substantially or entirely written by Astengo. Most of these papers were published either anonymously or under the name of the observatory director or another male colleague.
One paper, on the proper motions of a small group of southern stars, was published in 1894 under the initials P. A. alone. This is the only published work in which her name in any form appears in print during her lifetime.
She never married. She lived for thirty-three years in a small house on Calle Belgrano in Cordoba, two blocks from the observatory, with her sister Maria Teresa, who taught at a girls' school nearby. The sisters were known in the neighborhood as the senoras Astengo. They kept three cats and a small garden.
Petronila retired in May 1908 with a small pension of forty pesos a month, slightly less than half her final salary. The pension was the standard rate for female observatory employees of the period. She lived another eleven years.
She died on July 22, 1919, at the age of seventy-seven, of pneumonia. Her sister survived her by four years. The house on Belgrano was sold in 1923. The contents, including her library of approximately three hundred astronomical books and her personal observational notebooks, were sold at auction in Cordoba in May of that year.
The notebooks were purchased, fortunately, by a Cordoba bookseller named Domingo Berra who recognized their scientific value. Berra donated them to the observatory in 1934. They sat in the observatory's library, catalogued but not studied, for the next seventy years.
Garcia's 2003 paper was the first systematic study. Subsequent work by Pineda and by other historians of Argentine astronomy has filled in some of the picture. A short biography of Astengo was published by the Asociacion Argentina de Astronomia in 2014. A street in a Cordoba suburb was renamed in her honor in 2017.
The standard textbook of Argentine astronomical history, currently in its fourth edition, still does not mention her.
What she contributed is difficult to summarize in the categories that nineteenth-century science used to recognize. She did not discover a new planet. She did not propose a new theory. She did not direct an institution.
She did calculate, very accurately, the positions of tens of thousands of southern stars at a moment when those positions had not been calculated before. She did record, in her own observing notebooks, the positions of stars no one else was watching. She did write papers that were published under other people's names.
The catalogs she helped produce became the foundation of southern-hemisphere positional astronomy. They were used by every observatory in the southern hemisphere for the next fifty years. They are still cited in technical literature on stellar proper motions.
Her name, when it appears, appears in archives. A notebook in a humid room in Cordoba. A payroll register. A letter at Harvard. A bookseller's receipt from 1923. Garcia's paper, twenty-three years old now, citing all of these and assembling them into the portrait of a person who looked at the southern sky for thirty-five years and recorded what she saw.
The sky over Cordoba on the night of August 14, 1879, looked very much as it looks now. The star she recorded that night is still where she put it.
