NEW YORK, NY.- In the early 20th century, when Henrietta Leavitt began studying photographs of distant stars at the Harvard College Observatory, astronomers had no idea how big the universe was. Debate raged over whether all of the objects visible through the telescopes of the day were within our own Milky Way galaxy, or whether other galaxies — or “island universes,” as they were then called — might exist somewhere out in space.

Leavitt, working as a poorly paid member of a team of mostly women who cataloged data for the scientists at the observatory, found a way to peer out into the great unknown and measure it.

What’s now commonly called Leavitt’s Law is still taught in college astronomy courses. It underpinned the research of other pioneering astronomers, including Edwin Hubble and Harlow Shapley, whose work in the years after World War I demolished long-held ideas about our solar system’s place in the cosmos. Leavitt’s Law has been used on the Hubble Telescope and the James Webb Space Telescope in making new calculations about the rate of expansion of the universe and the proximity of stars billions of light years from Earth.

“All of those major discoveries rested on Leavitt’s discovery,” Wendy L. Freedman, a professor of astronomy and astrophysics at the University of Chicago, said in a phone interview, referring to the explosion of knowledge about space over the last century. “It’s the bedrock foundation of so much of what we do today in cosmology and astrophysics in general.”

What Leavitt achieved was essentially twofold. In a groundbreaking observation in 1908, she noticed that certain stars, called Cepheids, photographed in the Large and Small Magellanic clouds — two relatively nearby galaxies — had a distinctive pattern: The longer it took for the Cepheids to cycle through their variations, the brighter they were in magnitude. Then, in a paper in 1912, she laid out a mathematical formula to explain her observation, called a “period-luminosity” relationship.

That opened the door to a new kind of interstellar triangulation, as Cepheid variables emerged as a reliable way to calculate cosmic scale for Earthbound astronomers. Distances that before then were anyone’s guess suddenly had a formula, and the portrait that emerged was shocking — a universe hundreds of times bigger than most astronomers had imagined.

“She had this singular insight, a key to measuring distance in the universe, and that work had staying power,” Christopher D. Impey, a professor of astronomy at the University of Arizona, said by phone.

Leavitt’s life, beyond her work on the stellar variables, remains largely in shadow. She wrote few letters or other papers that survive, according to a short biography published in 2005 called “Miss Leavitt’s Stars,” by longtime New York Times science reporter George Johnson. And throughout her life she suffered from fragile health, with several long illnesses, including one that kept her away from Harvard for about a year. She lost her hearing in adulthood, and when she died of cancer in 1921, the value of her possessions totaled $314.91 (about $5,500 in today’s dollars), including a $5 desk and two mattresses worth a total of $10.

Despite her struggles, Johnson wrote, “She seemed to be content to be a small part of a greater thing called science.”

But between the quiet contours of her personal life, or perhaps in some ways because of them, Leavitt’s story has resonated — both in popular culture in recent years and among the family members descended from one of her sisters. (Leavitt herself never married or had children.)

A crater on the moon was named in Leavitt’s honor. Her image hangs in the Smithsonian’s National Portrait Gallery. A play about her life and work, “Silent Sky,” by Lauren Gunderson, has been performed around the world since its premiere in 2011 at South Coast Repertory in Costa Mesa, California.

Gunderson’s dramatization tells the story of Leavitt’s passion for astronomy and the struggles she faced, both in her health and in the male-dominated world of science.

“She cracked into something that was not only impressive scientifically but shifted an entire paradigm of thinking,” Gunderson said in an interview. “And that discovery was made by somebody who was not fully welcomed into the scientific community.”

In researching Leavitt’s life, Gunderson said she found a compelling element in the collective power of the women at the observatory and how they worked together and supported one another.

“They were not allowed to do the astronomical research that required the telescope or staying up at night surrounded by other men, but they did have this space that was theirs,” she said.

Betsy Hodges, the great-granddaughter of Leavitt’s sister, Martha Alvira Strong, grew up listening to family stories. Hodges, who was the mayor of Minneapolis from 2014 to 2018 and is now a writer and consultant on urban issues and racial equity, said her mother and grandmother instilled in her the idea that Leavitt’s achievements were made through ferocious focus and a belief in the importance of one’s work.

“Achievement for something you love is possible,” Hodges said in an interview. “That’s the lesson that I learned from her — she loved what she loved. She was so into those equations. She was so into watching those stars. She was so into it that she was willing to defy all kinds of expectations to continue to do it and to continue to contribute.”

Henrietta Swan Leavitt was born on July 4, 1868, in Lancaster, Massachusetts, the oldest of seven children. She was named for her mother, Henrietta Swan (Kendrick) Leavitt. Her father, George Roswell Leavitt, was a Congregational minister who presided over a church in Cambridge, not far from the Harvard campus, before taking church assignments in Cleveland and later in Beloit, Wisconsin.

Education, in a family that traced its roots back to early Puritan stock in colonial Massachusetts, was a deep constant. Henrietta’s father had received an undergraduate degree at Williams College and later a doctorate of divinity. One of her uncles was a mechanical engineer. She studied at Oberlin College in Ohio, then graduated in 1892 from the Society for the Collegiate Instruction of Women in Massachusetts, which would a few years later be renamed Radcliffe College.

Her course of study was mostly in the liberal arts — languages, art, philosophy and history — but in her final year before graduation, according to Johnson, she took an astronomy class. That apparently set a new direction in her life.

The class was taught by an astronomer who worked at the Harvard observatory, just up the street from her school, and she began volunteering there without pay after graduation.

In 1902, after traveling and living in Wisconsin and teaching art, she wrote to the Harvard observatory’s director, Edward Charles Pickering, asking if there might be a place for her back in Cambridge.

She was losing her hearing, she told Pickering, according to Harvard’s Center for Astrophysics, in a biographical portrait published on the 100th anniversary of her death. But perhaps, she said in her letter, because of her love of astronomy and her ability to fall so deeply into study, she seemed to notice even less of the world’s noise when under the spell of the stars.

“My friends say, and I recognize the truth of it, that my hearing is not nearly as good when absorbed in astronomical work,” she wrote.

Pickering hired her as a “computer” — a kind of cross between a clerk and a bookkeeper — tasked with looking at photographs taken by the astronomers through their telescopes and then measuring and calculating the relative positions of the stars and other celestial bodies. Computers were paid 25 cents an hour.

She died on a cold, rainy night in Cambridge, on Dec. 12, 1921. She was 53.

So quietly did Leavitt’s own star dim that when, in the mid-1920s, a Swedish mathematician wrote to her saying he intended to push her name in consideration of a Nobel Prize, he didn’t know she was already dead. Posthumous Nobels have only been awarded twice, according to the Nobel Foundation website, and have been banned entirely since 1974, unless the recipient died after the prize’s announcement.

This article originally appeared in The New York Times.