forgotten pages: story of how few female Harvard computers revolutionized our understanding of the universe | The Weather Channel – Articles de The Weather Channel
In the first story of this series, we learned how Antonia Maury helped us understand the stars better and fought for recognition for her work. In this article, let’s understand how Harvard’s brightest human computers have helped us better understand our universe.
From Fleming to How to Classify Cannon’s Stars
Along with Antonia Maury, many brilliant women joined in efforts to establish stargazing documentation to produce the HD Star Catalog in the 19th century. One of these ladies was Ms. Annie Cannon, who eventually took over the Henry Draper Catalog group. Annie began astronomy under the guidance of her mother, Jump Cannon, who was passionate about science. They had a little roof door in their house from where they could see the beauty of the stars. Her mother encouraged Annie to undertake scientific studies.
Annie studied physics and astronomy at Wellesley College and eventually landed in the Pickering group as an underpaid “human computer”. She joined the efforts of A. Maury, W. Fleming and later Henrietta Leavitt. This was the time when Maury had a disagreement with Professor Pickering over the allocation of credits to female researchers. Another disagreement was escalating, and it was between the ladies.
Ms. W Fleming developed a simple classification system in which stars were classified according to the abundance of hydrogen in their spectrum. The spectra with the strongest lines were classified as “A” stars, the next “B” the strongest, and so on up to the alphabet O, for which the hydrogen lines were weak. Finally, two decades later, astronomers realized that hydrogen lines are not a good indicator for classifying stars since these lines disappear from the visible light spectrum when stars get too hot or too cold. During this time, Ms. Maury devised a complex system based on the surface temperature of stars, classifying them as Type-a, Type-ac and so on. The differences became so great that Ms Fleming stepped down and stepped down as manager, which then passed to Ms Cannon. Ms. Fleming is now well known for two important contributions. One is the discovery of the famous horse’s head nebula in the constellation Orion, and the other is the discovery of a white dwarf star.
The new manager, Ms Cannon, carefully examined the data and understood the perspectives of her two predecessors. She simplified the spectral classification and based it on the surface temperature of stars. So, high temperature stars were called Class ‘O’, then B, then A and so on until class M stars darkened. This scheme is now known as the Harvard Classification and even today is followed as the standard for stellar classifications. Spectral classes are therefore OBAFGKM, commonly memorized as Oh, Be A Fine Girl Kiss Me! (Guy instead of Girl, for those who wish to substitute themselves!). Recently the mnemonic is now changed to: “Oh Boy! An F grade kills me! “
Annie Cannon was the fastest star rating person and she could easily rate 5,000 stars per month. During her career, she identified and cataloged 350,000 stars. In 1921, Cannon became the first woman to receive a doctorate in astronomy from the University of Groningen. She later became the first woman to receive an honorary degree from the University of Oxford. In 1922, the International Astronomical Union adopted Cannon’s method as the official spectral classification system. In 1923, Cannon was voted one of America’s 12 Greatest Living Women by the National League of Women Voters. After decades of hard work, Cannon was finally appointed a permanent professor at Harvard College Observatory in 1938.
Leavitt’s contribution to our understanding of the universe
At the same time, another outstanding astronomer was working at Harvard Computer, Henrietta Swan Leavitt, and she focused on variable stars. She began to study the stars of the constellation Cepheus and found a type of variable star called the type of Cepheus. A variable star changes its brightness in a fixed period of time. For example, the famous Algol star changes almost five times its apparent brightness in about three days. So today it is a bright star, while tomorrow night it will be five times weaker, and on the third day it will be bright again.
Mrs. Leavitt discovered an astonishing fact for Cepheid-type variables (named after the star d-Cephei in the constellation Cepheus): the period of these stars is proportional to the luminosity. The higher the brightness, the longer the pulse period. Now if you know the period of variation, you can find the brightness, and from that we can easily find the distance to the star. So, for stars located at very great distances, astronomers now had a way to measure distances if you find a Cepheid-like variable. This relationship is called the Period-Luminosity Law, and it has opened doors for measuring the distances of distant stars.
Henrietta then went to study more than 2000 stars of this type in the nearby “clouds” called Large Magellanic Cloud (LMC) and Small Magellanic Cloud (SMC). She discovered that the distances between these two objects are very large compared to most stars or “nebulae” in the neighboring region. So came the concept of the galaxy, and ultimately astronomers confirmed that LMC, as well as SMC, are outside of our Milky Way galaxy. Today we know that they are companion satellites of our galaxy.
The beautiful Andromeda galaxy was found an astonishing 2.2 million light-years away, so we understood that the Milky Way is one of many galaxies in the universe. The concept of how our universe looked changed dramatically after Leavitt’s findings. Professor Harlow Shapley (who invited Anni Cannon) pulled out a working model of the Milky Way’s spiral arm. Interest in the field of cosmology has grown exponentially. Based on the methods of Leavitt, Cannon, Maury and others, astronomers measured the distances of distant galaxies and also understood that all galaxies have high speed in the universe.
In 1916 Professor Einstein came up with the theory of general relativity. Physicists and mathematicians used this revolutionary theory and began to develop models of our universe. Einstein himself came up with solutions for his theory, and to his surprise, he discovered that the universe is expanding and not static! Such was the firmness of the concept of a static universe that he introduced a constant into his theory and made the universes a “static universe”. His contemporary scientists were not bound by such stationary ideas, and mathematician Alexander Friedmann came up with a model of the universe which was expanding and could contract in the future. So the debate over how the universe was heating up.
Edwin Hubble applied Leavitt’s methods to measure galactic distances and, at the same time, began to measure the speed at which galaxies move. To his surprise, he discovered that all galaxies were moving away from each other and the further the galaxy was, the faster its escape speed. He thus concluded that the universe is expanding! Sadly, Mrs. Leavitt was not alive to see her work’s greatest triumph. She died in 1921 at the age of 53.
The work done by these ladies in the late 19th and early 20th centuries was revolutionary. This was done in a very depressing situation with insufficient pay, no assurance of continuity of employment, minimal credit for the work, and no scientific benefit other than the pleasure of doing things. It took great zeal for their work and maybe hope that the world will one day recognize their work. Today, when astronomers use these concepts, we hardly think about who invented these ideas. Even today, many scientists forget to attribute the work to these brilliant female computers.
Nevertheless, the brilliance of their ideas and the simplicity of their methods are impossible to forget. These Harvard computers continue to shine as some of the brightest stars in astronomy!
This article is part of a two-part series of articles on World Space Week 2021. The first article in the series can be accessed here:
Story of how a Harvard computer woman spoke to the stars and carved her name on the moon
Dr Abhay Deshpande is a Senior Scientist (Physicist) working for SAMEER, MeitY R&D Laboratory, Government of India. He is also the honorary secretary of Khagol Mandal.
This article is a guest column reflecting the views of the author and does not necessarily represent the official views of The Weather Channel.
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