Henrietta Leavitt

Biography of Henrietta Leavitt American astronomer who, in the late 19th century, discovered a method of measuring distances to stars. She found a ruler to measure the size of the Universe.

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Her discovery is the cornerstone that revolutionized our knowledge of the Universe, expanding it to limits not previously imagined. It is because other astronomers could discover that there are millions of galaxies like ours.

Henrietta Leavitt’s family and early life

Henrietta Leavitt was born in Lancaster, Massachusetts, United States, on July 4, 1868.

Henriette Leavitt was the daughter of a Congregationalist priest of the “United Church of Christ“.

Henrietta’s father was the brother of Erasmus Darwin Leavitt, an outstanding engineer of her time.

Everything about Henrietta Leavitt’s personal life is unknown, beyond the fact that it is known that she never married or raised a family.

She studied at the Radcliffe Institute, a university for women, which is located in Cambridge (Massachusetts) and was attached to Harvard University.

There she met Charles Pickering, one of the most important scientists of the time, and director in those years of the Harvard Astronomical Observatory.

At 24 years of age, in 1892, she graduated as a graduate in higher studies.

A short time later, she suffered a terrible illness, which caused her a profound deafness that lasted her whole life.

Charles Edward Pickering
Edward Charles Pickering astronomer, discoverer of stars and the worth of women. Credit: Popular Science Monthly.

Henrietta Leavitt calculator at Harvard

The following year, when Henrietta recovered from the disease, she volunteered to work at the Harvard College Observatory. It was a way to continue related to the world of science.

There, since 1886, a group of women performed relatively mechanical tasks, meticulously examining photographic plates or making tedious calculations. They were called the “Harvard calculators” or also, the “Harvard computers“.

Henrietta Leavitt was hired full time, to work 6 days a week, 7 hours a day, with a salary of 25 cents an hour.

Astronomer Harvard
Edward Pickering and his team of calculators in the Harvard College room. Credit: Wikipedia.

Edward Pickering and the Harvard calculators

In some articles, Charles Pickering is accused of being a character who took advantage of the work of this team of women, and who took full credit for the discoveries they made. It seems that these assessments are wrong.

In the spring of 1879, in the city of Boston, 22-year-old Scottish immigrant Williamina Fleming was pregnant, alone, and had no place to live; penniless, she had to immediately find a job, whatever it was.

She found work and shelter in the domestic service of the home of Professor Edward Pickering, Director of the Harvard University Observatory.

Before long, the teacher encouraged her to travel to Scotland, to give birth in her family’s home, supported by her loved ones. He promised to receive her again as soon as she wanted to return.

Williamina Fleming
Williamina Fleming had an attractive face, with bright and vivid eyes. She radiated vitality. Credit: web harvardmagazine.com

When Williamina knocked on her door again carrying her son, in April 1881, Edward Pickering offered her a job at the Harvard Observatory. Not as a maid, but as an assistant in administrative tasks and to do routine calculations.

When Edward Charles Pickering took charge of the Observatory, she embarked on the institution in an unprecedented challenge: the complete cataloging of the stars of the sky.

Thanks to his prestige and his gift of people, he managed to get Boston’s fortunes involved in financing the construction of a next-generation telescope at Harvard, and a similar one in Arequipa (Peru). Thus he managed to obtain information from the stars of both celestial hemispheres.

It soon became apparent that such an effort far exceeded the capabilities of Pickering and his assistants. The accumulation of mountains of glass plates coming from the two telescopes was absolutely beyond reach for the few men available.

In 1886 Pickering had an unexpected and brilliant idea, based on his first experience with an intelligent woman like Williamina Fleming. He raised more funds and hired a team of nine women to carry out routine calculations to analyze star photographs and classify spectra on photographic plates. It was a revolutionary decision, since until then women had been prohibited from accessing university facilities.

Astronomer Harvard
Female astronomers at Harvard. Credit: Harvard University Archive

Without a doubt, for these young women it was a more stimulating job than cleaning in a house or working in a factory.

Women trained in the women’s universities in the area arrived, and the team began to stand out for its efficiency and sagacity.

It was a magnificent team of human calculators that came to be known as “the Harvard calculators“.

They had access to the university space. Edward Pickering knew how to appreciate the worth of these women and managed to make them all work together in a room for them.

In addition, Pickering allowed creative work to be done on their own, in addition to their routine work.

The contributions these women made to astronomy are extremely remarkable. Especially Williamina Fleming, Annie Cannon and Henrietta Leavitt.

Given the customs of the time, the works of these calculators were overshadowed and unknown.

Edward Pickering was unable to overcome these base contempt for women. For example, when Annie Cannon did an incredibly wonderful job, he proposed to the President of Harvard University that she be given an official appointment.

The president only authorized Pickering to offer Annie Cannon a “conservative astronomical photograph” position. Nor did the university president authorize the name Annie Cannon to appear as a co-author of the Harvard Observatory’s catalog of stars, as requested by Professor Edward Pickering.

In 1893 Henrietta Leavitt joined the “Harvard Calculators” team. She was especially gifted for this job because, in addition to her intelligence and tenacity, she suffered from an incipient deafness that helped her to fully abstract herself in her work.

Over the years, Henrietta filled hundreds and hundreds of notebooks with notes of what she observed on the thousands of plates she studied.

Great discovery by Henrietta Leavitt

Henrietta Leavitt was to record the data for each star, including its size (related to brightness) and compare it with that obtained from the same space sector but at different times of the year.

One day, in 1904, when she was cataloging a crystallographic plate of the “Little Magellanic Cloud”, she observed a certain pattern in the behavior of the variable stars that were in the constellation of Cepheus.

magallanes cloud
The Great Magellanic Cloud was one of the wonders Hernando de Magallanes discovered when he circumnavigated Earth. Credit: web observatorio.info

Variable stars are those that vary their luminosity in a specific period of time. Cepheids, are the variable stars of the Cepheus constellation.

Excited by the discovery, Pickering commissioned more plates, and for four years Henrietta Leavitt kept an eye on the characteristics of these stars.

In 1912, Henrietta Leavitt wrote a three-page paper titled “Periods of 25 Variable Stars in the Small Magellanic Cloud“.

In it, she explained that, according to her data, the Cepheids flickered with a regular rhythm and became brighter the longer their period was, which seemed to happen in a quite predictable way. This claim that the brightest stars have the longest periods ended up totally revolutionizing astronomical science.

This short article, which has been fundamental in astronomy, was published signed by Edward Pickering, although it began with the note “this work has been prepared by Miss Leavitt“.

The article ended by concluding that Cepheids that had the same pulsation period also had the same luminosity. With this simple correlation between pulsation period and luminosity, she established the great rule that allowed to begin to measure the size of the Universe.

A year later, many more relative and absolute distances between stars could be determined thanks to the patterns discovered by Leavitt.

A way to measure the distance between very distant stars had been discovered quite accurately.

Thanks to this new method, in 1918 the size of the Milky Way was calculated.

Milky way
Self-portrait of the astronomer Alan Fitzsimmons, on May 13, 2013. Credit: ESO / A

The traditional method of calculating the distances of star bodies from Earth was parallax, a spatial trigonometry system invented by the Greeks. This method only served to measure distances within the Solar System.

What was beyond escaped our knowledge and prevented us from knowing the size of the Universe.

Some stars were known to appear to be the brightest than others, but there was no way of calculating how far apart they were.

In 1923, Edwin Hubble combining the ideas of Henrietta Leavitt’s work with discoveries made by other astronomers, astonished the world with the revelation that a spot seen in the sky was a huge galaxy made up of millions of stars and with a diameter of 150,000 light years: it was called the Andromeda galaxy.

Andromeda Galaxy
The Andromeda galaxy discovered by astronomer Edwin Hubble. Credit: Wikipedia

Very soon after, it was revealed that the Small Magellanic Cloud was 30,000 light years away.

Astronomer Harlow Shapley wrote saying that “the Magellanic Clouds had been looked at for 400 years, but they began to be seen in the early 20th century.” This spectacular advance was the work of Henrietta Swan Leavitt, who “seated at a work table at the Harvard Observatory studied with her lens a confusing aglomeration of black dots on the glass plates“.

We now know, thanks to the patterns formulated by Henrietta Leavit, that the Universe is made up not only of our galaxy, the Milky Way, but of billions of other distant galaxies.

Millions galaxies
There are an estimated more than 100 billion galaxies. Credit: Wikipedia

An estimated one in 10 variable stars known to astronomers today was first studied by Henrietta Leavitt.

Last years of Henrietta Leavitt

The great astronomer Henrietta Leavitt died of cancer in 1921, at the age of 53. Shortly before, she had left a will bequeathing all her property and possessions to her mother. The total value of her estate was $ 344.89.

Henrietta Leavitt could not read the letter that four years after her death, without knowing that she had died, the Swedish mathematician Gösta Mittag-Leffler sent her to nominate her for the Nobel prizes.

Mittag-Leffer’s intention was to propose Henrietta Leavitt to be nominated for the Nobel Prize for her work on variable stars and calculations of stellar distances.

However, and since the Nobel prizes cannot be awarded posthumously, she was never nominated.

The Leavitt Lunar Crater owes its name to Henrietta Leavitt.

The asteroid (5383) Leavitt (7 km in diameter) bears this name in her memory.

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