Development of the HR Diagram

Henry Draper was an amateur New York astronomer who, in 1874, invented a wonderful instrument for studying the spectra of stars, called the Spectroscope. With this device, it was possible to place a diffraction grating over a telescope lens and take a photograph of the star's absorption spectrum. Draper wanted to photograph the light from different stars and look for relationships among them. Unfortunately, he died at age 42 and did not live to discover any such relationship. His wife made a very large contribution of $400,000 to Harvard University in her husband's name to continue his passion. The University hired Edward C. Pickering to continue the study of stellar spectra.

 

 

E. C. Pickering (left) spent several years of tedious work and results as well as the pace were poor at best. One day he loudly complained to his team how slothful they were and that "my own Scotsmaid could do a better job than you." The team members quit and Pickering was without assistance. With nowhere to turn, he talked to his maid and offered her a job. Williamina Fleming took the challenge as a personal opportunity and photographed the spectra of over 5000 stars. Indeed, she discovered that the stars could be grouped into 4 types, A, B, C, and D, based upon their asorption spectral lines. Fleming worked long and late hours from her little office window at Harvard's Observatory. She would often forgo a bath or the maintaining of her hair because she would become so engrossed in her work. She even ignored the swarms of mosquitoes that rushed in her open window, but Pickering was so pleased with the efficiency demonstrated by Fleming that he hired more women to his staff. He claimed that these women were much better at spectroscopy than men because they did not mind tedious work, were willing to work for less money, and made no haughty complaints as did his men. The team of women grew and soon was featured in local newspapers as "Pickering's Harem," seen in the image below. One look will tell that this group was a stern-looking group of women, but did they make exceedingly important contributions to Astronomy.

 

 

This picture which includes Edward Charles Pickering, the Director of Harvard College Observatory (1877-1919), was taken on 13 May 1913 in front of Building C, which faces north. At that time it was the newest and largest building of Harvard College Observatory. It was specially built of brick to protect the astronomical data and glass negatives from fire. Since the astronomical photographs were stored on the ground floor and most of the women worked on the top floor, the building had a dumb waiter to convey the plates up and down. The women all worked in a large room on the east end of the third floor. Pickering had his offices on the west end across the central hallway. All the other men worked on the lower levels.
At the far left of the photograph is Margaret Harwood (AB Radcliffe 1907, MA University of California 1916), who had just completed her first year as Astronomical Fellow at the Maria Mitchell Observatory. She was later appointed director there, the first woman to be appointed director of an independent observatory. Beside her in the back row is Mollie O'Reilly, a computer from 1906 to 1918. Next to Pickering is Edith Gill, a computer since 1889. Then comes Annie Jump Cannon (BA Wellesley 1884), who at that time was about halfway through classifying stellar spectra for the Henry Draper Catalogue. Behind Miss Cannon is Evelyn Leland, a computer from 1889 to 1925. Next is Florence Cushman, a computer since 1888. Behind Miss Cushman is Marion Whyte, who worked for Miss Cannon as a recorder from 1911 to 1913. At the far right of this row is Grace Brooks, a computer from 1906 to 1920.
Ahead of Miss Harwood in the front row is Arville Walker (AB Radcliffe 1906), who served as assistant from 1906 until 1922. From 1922 until 1957 she held the position of secretary to Harlow Shapley, who succeeded Pickering as Director. The next woman may be Johanna Mackie, an assistant from 1903 to 1920. She received a gold medal from the American Association of Variable Star Observers (AAVSO) for discovering the first nova in the constellation of Lyra. In front of Pickering is Alta Carpenter, a computer from 1906 to 1920. Next is Mabel Gill, a computer since 1892. And finally, Ida Woods (BA Wellesley 1893), who joined the corps of women computers just after graduation. In 1920 she received the first AAVSO nova medal; by 1927, she had seven bars on it for her discoveries of novae on photographs of the Milky Way.
Barbara L. Welther published the photograph and some of the text in a note about "Pickering's Harem" in Isis 73, 94 for March 1982.

Pickering hired the niece of Henry Draper's widow. Antonia Maury was well-educated in Physics, having earned her collegiate degrees from Harvard, as well as the esteem she enjoyed from her wealthy donar aunt. Maury treated Fleming as an uneducated lower class person who must know little about the workings of Astronomy. While Fleming clearly saw 4 major star groupings, Maury discerned 22 distinct groups of stars ... A - V. The two women were frequently at odds, and while Pickering may have personally favored Fleming's opinion, he often deferred to Maury due to her education and personal influence.

Pickering then hired Annie Jump Cannon and asked her to take the spectroscopy work to a new level. Within 5 years, Cannon photographed over 400,000 stars, and catalogued 225,000 stars! From her vast experience and immense photographic record, Cannon offered a compromise between the systems of Fleming and Maury. Several letters were dropped or merged and the system developed was based on the strength of the hydrogen absorption lines. The system is familiar to all students of Astronomy, and stars fall into classes --- O B A F G K M. Recent discoveries have extended it to a new class of even cooler stars in the grouping "L."

 

 

 

 

Pickering, Fleming, Maury, and Cannon noticed that O stars showed strong ionized Helium lines, B stars showed strong Hydrogen lines and neutral Helium, A stars showed strong Hydrogen lines, while F, G, K, and M progressively show stronger ionized metal lines, then neutral metals lines, and finally molecular bands. It was also obvious that the stars were grouped according to their temperatures, with the hot O class at 50,000 K down to the cool M class at 2000 K, with our Sun in the middle at 6000 K. As the spectroscopy improved, Cannon broke each spectral letter class into subgroups of 0-9 to discriminate better between then. The Sun is a G2 star, cooled than a G0, but warmer than a G9. A comparison of the spectra of 7 different stars from the 7 spectral classes is found below. The image to the right of the actual spectra is an artistic rendition of the classes, and also idealized. I will refer to this picture during one of the chat times

The image you see below is with the actual colors of visible light and the absorption lines within, as well as a nice set of element labels.

I have put these three spectral images into this page so you can see what astronomers are looking for and at with their images from the spectroscope. To me, this stuff is really cool, but even better is what we can discern from this information.

I CANNOT STRESS ENOUGH THE VALUABLE CONTRIBUTIONS OF THIS GROUP OF WOMEN AT THE HARVARD COLLEGE OBSERVATORY. WHILE MANY LOOK BACK AT THESE WOMEN IN SCIENCE AS AN ANOMALY OF THE TIME, AND MAKE NUMEROUS REFERENCE TO THE STEREOTYPE OF CHEAP LABOR AND TEDIUM OF WOMEN IN THE WORKPLACE, MUCH LESS SO AT AN ACADEMIC SETTING SUCH AS HARVARD, PICKERING SHOULD BE CREDITED AS BEING ONE OF THE PIONEERS OF THE LARGE TEAM SCIENCE CONCEPT. ADDITIONALLY, THESE WOMEN PAVED THE WAY FOR OTHERS WHO FOLLOWED, OPENING THE DOOR TO OPPORTUNITIES FOR WOMEN IN ASTRONOMY AS WELL AS THE OTHER SCIENTIFIC DISCIPLINES.

Please move forward now to HR Diagram2, or return to the Introduction to the Sun, or to the Syllabus.


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