From a maid to a female astronomer, she made the professor's complaint "My maid does a better job than you" come true... | Women's Day

Long before computers were invented, the word "computer" was already in existence, referring to calculators who performed mechanical statistical and computational work. The earliest written record of a calculator dates back to 1613. Renaissance astronomers often jokingly called themselves "mathematicians," and they would often hire a "calculator" to help calculate planetary positions, and many famous astronomers of the time (such as Johannes Kepler) worked as calculators for their mentors. "A maid can do this job better than you!"

In that era, as modern astronomical research gradually got on track, massive amounts of astronomical data poured into observatories, causing a lot of redundancy. Many observatories had to expand the number of computer recruits to ensure work efficiency. However, this put the observatories under tremendous financial pressure.

Edward Charles Pickering, then director of the Harvard College Observatory (later the Harvard-Smithsonian Center for Astrophysics), was also facing severe problems of understaffing and funding shortages.

At that time, women were usually excluded from scientific research activities due to the constraints of the times, and computer operators were basically only male employees. However, the number of female workers was no less than that of men, and Pickering also noticed the potential of women as computer operators. Pickering once mentioned that he was "very frustrated with the inefficiency of his male assistants, and even his maids could do a better job of sorting and calculating." At that time, the wages of male employees were usually much higher than those of women, so under the premise of the same budget, Pickering could hire more female computer operators to participate in the work.

Pickering was naturally a man of his word and of his action. The first female computer he hired was indeed the housemaid, Williamina Fleming .

Wilhelmina Fleming. Image source: Wikipedia

Fleming worked as a student teacher at the age of 14. After becoming a maid, she was recommended by Pickering's wife to start part-time administrative work at the observatory. She then joined the Harvard Computers team as a founding member under Pickering's guidance.

In 1886, Mary Anna Draper, widow of astronomer Dr. Henry Draper, generously donated a large sum of money and Dr. Drake's telescope to the Harvard Observatory to assist in providing employment for women and to help complete her late husband's research projects.

Soon after, women such as Antonia Maury, Anna Winlock and Annie Jump Cannon also joined the group of Harvard computers.

Harvard computer workers at work, including Leavitt, Cannon, Fleming, and Maury. Image source: Harvard University Observatory

Within a few years, Pickering and his team of computer engineers completed and published the world's first large-scale star catalog of stellar spectra, the Henry Draper Catalog (HD), which included more than 10,000 stars. This star catalog has been improved and modified several times and has become the basis of today's stellar spectral classification system.

Pickering hired more than 80 female computers to assist in his work. The astronomical community even jokingly called the Harvard computer team "Pickering's Harem." However, the work abilities of these female computers were extremely outstanding and they were destined to leave a significant mark in the history of modern astronomy.

The ruler they found

In the early days of astronomy, distance measurement mainly relied on the trigonometric parallax method. This method requires observers to measure the elevation angle of a celestial body at two different time points during the year when the Earth revolves around the Sun, and use these two data to calculate the distance between the celestial body and the Earth. However, since this method requires extremely high observation accuracy, the range of distances that can be accurately measured is basically limited to the Milky Way.

It is worth noting that people at that time had not yet formed the understanding that the scope of the universe far exceeded the Milky Way.

In 1903, Henrietta Swan Leavitt received a reply from Pickering and resolutely ended her job as an art assistant in Wisconsin and returned to Harvard University Observatory as a "Harvard computer." For her, this might be her last chance to realize her ideal.

Henrietta Swan Levitt. Image source: Wikipedia

Levitt attended Radcliffe College (one of the Seven Sisters Colleges in the United States, later merged into Harvard University) and received an A- in the astronomy course. However, something unexpected happened. Levitt contracted a serious illness during her graduation trip, which caused progressive hearing loss. In the following decades, she almost lost all her hearing.

Although she tried to study under Pickering, pursue a master's degree in astronomy and join the Harvard computer team, the pain forced her to give up her studies and leave for Wisconsin, where she worked as an art assistant at Beloit College. Six years later, as her condition worsened, Levitt realized that she was no longer qualified for any work, so she wrote to Pickering for help and applied to return to the Harvard Observatory.

Pickering agreed.

Considering the communication problem, Pickering did not assign Leavitt to carry out research tasks that required frequent communication, such as star classification. Instead, he assigned her to study the variable stars observed in the Large and Small Magellanic Clouds. The main content of her work was to measure and record the stellar brightness captured in the observatory's photographic plates. Because the star classification system was not perfect at that time, it was very difficult to identify variable stars, which required researchers to be extremely patient and focused.

The inability to hear the sound seemed to help Levitt stay focused at this time, and she was so fast in finding variable stars that she found 1,777 variable stars in a large number of photos, 47 of which were Cepheid variables, which increased the sample statistics of variable stars at that time by several orders of magnitude.

Cepheid variables are stars whose brightness changes periodically, changing between the brightest and the darkest over and over again like breathing. Since the first discovered and widely studied variable star of this type was Delta Cephei, which is Cepheid I in the ancient Chinese astronomical naming system - Cepheid was one of the ancient star officials, belonging to the Wei Mansion in the northern seven of the twenty-eight mansions - this type of variable star represented by Delta Cephei is called a Cepheid variable star.

When compiling the results of Cepheid variables, Levitt noticed that there seemed to be a certain pattern in the period and strength of the brightness changes of Cepheid variables, so she spent several years compiling and analyzing the relationship between the luminosity and light variation period of Cepheid variables.

Leavitt was very lucky. The variable stars she observed were in very ideal positions. They were all in the Small Magellanic Cloud and were approximately the same distance from the Earth, so the effect of the distance factor on luminosity was basically the same.

Leavitt was pleasantly surprised to find that brighter variable stars tend to have longer light variation periods. She published these findings in a 1908 paper, and in the following years confirmed that Cepheid variable stars and other celestial bodies have a light variation period-light intensity relationship (period-luminosity relationship), that is, the luminosity of pulsating variable stars is proportional to the logarithm of their period. This relationship was later called Leavitt's law.

Leavitt then realized that although the distance to the Small Magellanic Cloud was unknown at the time, under the premise that the period-luminosity relationship was valid, as long as the distance between any Cepheid variable star and the Earth was known, the distances between all Cepheid variable stars and the Earth could be inferred.

Small Magellanic Cloud. Copyright image. Reprinting may cause copyright disputes.

This is a ruler, a celestial ruler that can measure the universe. This celestial body that can be used as a distance scale is later called a standard candle.

The light emitted by celestial bodies gradually attenuates with distance as it propagates in the universe. Therefore, as long as we know the actual luminosity of the corresponding celestial bodies, we can infer their distance based on the observed luminosity, just like the candle flames of known standard brightness in the universe. This is the origin of the name of the standard candle.

These standard candles constitute the distance scale in the universe. Any celestial body can be determined by the standard candles near it. The observation of the properties of stars and galaxies and various studies in cosmology all rely on the distance measurement involving standard candles.

Cepheid variables, whose actual brightness can be determined as long as the period is known, are a good type of standard candle because they are widely present in almost all galaxies. Not only this type of variable star, but also Williamina Fleming, a founding member of Harvard Computers, determined the variable nature of RR Lyrae when collating data, as Pickering's work at the same time was largely about variable stars (because RR Lyrae is the brightest among its type of variable stars, this type of variable star was eventually named RR Lyrae type variable star), which is also a standard candle commonly used today.

In 2023, Chinese astronomers made a new breakthrough in the study of RR Lyrae variables. They found that the double-period RR Lyrae variable stars may become the most ideal standard candles. The measurement error of celestial distances can be reduced to less than 2%, greatly improving the accuracy of astronomical measurements.

Under the leadership of these outstanding Harvard computer scientists, the accuracy of cosmic distance measurement has been continuously improved, and human vision has been pushed to deeper and deeper space. Female scientists have proved their indispensable role in astronomical research with their outstanding professional ability and scientific research enthusiasm.

However, this process was extremely difficult. Many female calculators were even graduates of astronomy, but their salaries were only comparable to those of unskilled workers , usually between 25 and 50 cents per hour (even as of 2022, it was only $7 to $15). In Pickering's time, the workload of astronomical calculations was very huge, and the demand for calculators was also very high. Some women even offered to become Harvard calculators for free in exchange for the qualification to engage in astronomical work.

With the continuous advancement of women's cause, more female scholars have been able to formally enter the field of astronomical research, leaving their own shining stars in the starry sky of human exploration of the universe.

Planning and production

Author: Mao You is a PhD student at the National Astronomical Observatory of the Chinese Academy of Sciences

Review丨Han Wenbiao, Researcher at Shanghai Astronomical Observatory, Chinese Academy of Sciences

Planning丨Yang Yaping

Editor: Yang Yaping