Harvard Computers: Unsung Pioneers of Modern Astronomy

Harvard Computers

Before electronic computers were originated, the word “computers” referred to the “ones who compute”, the person who performed and processed the tedious calculations, typically the females. Teams of women performed the onerous task of transcribing raw data into analyzed and verified records. The “Harvard computers” were a group of remarkable women who operated astronomical data at the Harvard Observatory in Cambridge, Massachusetts, United States. Harvard computers were led by Edward Charles Pickering, who was the director of Harvard Observatory since 1877. After his death in 1919, Annie Jump Cannon was entitled as the team lead, steering the crew at the helm.

The Women Who ‘Upstaged’ Themselves

The Harvard computers hired by Pickering were sort of low-paid clerks doing their clerical work. Their role was to look over photographic plates to classify stars by measuring the brightness, comparing the positions of stars between those plates, and determining the color of stars. Among these “computers”, some were astronomy graduates working with such efficiency to bring some of the key concepts in astronomy to light. Annie Jump Cannon, Williamina P. S. Fleming, Antonia Maury, Henrietta Leavitt, and Florence Cushman were some notable data scientists and astronomers who mapped the night sky paving the way for women in science to step forward.

Edward C. Pickering and the Harvard Computers in a group shot taken in 1913
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The computers manually stored the data, classifying hundreds of thousands of stars portrayed in glass plates. They chronicled each fleck of stars, nebulae, and other space bodies while carefully recording those to map the sky. Here’s to those women, the honorable women who made groundbreaking findings, despite derogatory comments and ridicules by men, who moved forward lighting the path for generations of future scientists.

Harvard Computers: A Look Back, Unearthing Some Notables

Annie Jump Cannon: Census Taker of the Sky

Known as the “Census Taker of the Sky”, Annie Jump Cannon was an American astronomer and pioneer of star classification. She was a trailblazing astronomer who manually recorded a massive number of star catalogs comprising of around 350,000 stars, discovering 300 variable stars (the stars that fluctuate its brightness as seen from the Earth), five novae (the stars shining with a sudden increase in brightness and then returning slowly to its original state over a few months), and one spectroscopic binary. She revolutionized the classification of stars by developing and refining a system based on temperature as the main feature of their spectral characteristics taken into account.

Annie Jump Cannon
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Harvard Spectral Classification

The classification of stars is known as stellar classification in astronomy. The stars are classified based on their spectral characteristics. The accepted stellar classification system is a combination of two classification systems, the Harvard system based on the temperature of star surface and the MK system based on the luminosity of stars.

Annie Jump Cannon developed this scheme by re-ordering the prior alphabetical system, the Draper system in which the stars were assigned a type A to Q based on the intensity of hydrogen spectral lines. However, it was found that there was overlap between the types and therefore, this was modified by Annie Jump Cannon to develop Harvard System. The stars are divided into groups according to their spectral characteristics by letters of the alphabet and subdivided by numerical values. There are seven main classes of stars according to this classification.

Harvard Spectral Classification
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The surface temperature of the stars decreases moving from O-type stars to M-type stars, from hottest to cooler stars. The subdivisions are denoted by Arabic numerals (0-9), where 0 denotes the hottest stars in a class. For example, O0 denotes the hottest stars in the type O stars and O9 denotes the coolest in that class. Our sun is classified as a G2 star according to the system.

Harvard Stellar Classification
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Henrietta Leavitt: To Measure Far-flung Corners of the Universe

Henrietta Leavitt was an American astronomer who is little known but contributed largely to the betterment of astronomy while working as a “computer” in the Harvard Observatory. She is a person who made a groundbreaking discovery yet received neither recognition nor plaudits during her lifetime.

Henrietta Leavitt
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Working as a computer, she cataloged, recording the brightness of the stars through photometry, and other celestial bodies just as her peers did. She discovered while proceeding with her typical book-keeping job, that she could accurately and consistently relate the period of a given variable star’s brightness cycle to its absolute magnitude. This discovery made its way to determine the distance to those stars from the Earth, unveiling how to measure the universe! However, she was merely mentioned when this far-reaching breakthrough was published. Astronomer Edwin Hubble later used her method to measure the distance of the Andromeda galaxy from the Earth.

In 1912, a paper was published by her denoting the relationship between the periods and the luminosity of a sample of the Cepheid variable in the Magellanic Clouds. These Cepheid variable stars are intrinsic variables, a class of pulsating stars, which are considered as one of the best methods to measure the distance in the universe.

Leavitt wrote in her paper;

“It is worthy of notice that the brighter variables have the longer periods.”

A graph plotted by Leavitt showing the relationship between logarithms of star periods and their respective magnitudes of Cepheids
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In her paper, she plotted a graph relating the logarithm of the period of the corresponding Cepheid and the magnitude using the data she collected from 25 Cepheids in the Small Magellanic Cloud. She unlocked the door to the universe and her work was crucial to the astronomy developments paving the way to grasp the scale of the universe.

Florence Cushman

Florence Cushman was also an American astronomer who specialized in stellar classification and worked at the Harvard Observatory from 1918 to 1937. She contributed her waking hours to catalog, analyze and classify the astronomical data and she is known for her findings regarding the positions and magnitudes of the stars listed in the Henry Draper Catalogue in the 1918 edition.

She applied the objective prism method to analyze the stars.

The Heroines of an Untold Journey

The Harvard Computers worked tirelessly at a time when the scientific profession was considered exclusively a male prerogative. They were not given the proper recognition even if they bestowed novel concepts that are still being used even today. They were the trailblazers who illuminated the path towards unlocking the mysteries in the universe.

We should be grateful for what they did, admire their passion and contribution, and amidst everything we should get inspired, ignore the naysayers and step out breaking the boundaries. The universe is out there eagerly waiting for you to discover it!


  • 01. Bergquist, C. (2016, December 9). The Female Astronomers Who Captured the Stars. Science Friday. https://www.sciencefriday.com/segments/the-female-astronomers-who-captured-the-stars/
  • 02. Howell, E. (2016, November 10). Harvard’s “Computers”: The Women Who Measured the Stars. Space.Com. https://www-space-com.cdn.ampproject.org/v/s/www.space.com/amp/34675-harvard-computers.html?amp_js_v=a6&_gsa=1&usqp=mq331AQKKAFQArABIIACAw%3D%3D#aoh=16334632537949&referrer=https%3A%2F%2Fwww.google.com&_tf=From%20%251%24s&share=https%3A%2F%2Fwww.space.com%2F34675-harvard-computers.html
  • 03. Swinburne University of Technology. (n.d.). Harvard Spectral Classification | COSMOS. Swinburne University. Retrieved October 9, 2021, from https://astronomy.swin.edu.au/cosmos/h/harvard+spectral+classification

Image Courtesies

01. Featured Image: Designed by Dasith Tilakaratna (SEDS UOC). Images resourced from https://bit.ly/3apdC2l and https://bit.ly/3oLyU2F.
02. Image 01: https://bit.ly/302UXaQ
03. Image 02: https://bit.ly/3mxQV1T
04. Image 03: https://bit.ly/3Bh3W67
05. Image 04: https://bit.ly/3ad1yBm
06. Image 05: https://bit.ly/3oBMC8d
07. Image 06: https://bit.ly/3oBMZj7

Article by F.B.I. Nimeshi (2nd Year Undergraduate)

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