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Essay by Debra Meloy Elmegreen

Professor of Astronomy on the Maria Mitchell Chair

Maria Mitchell, America’s first female astronomer, was also a pioneer of astrophotography and the first scientist to photograph the Sun on a daily basis. She gained international recognition in 1847 after winning a competition to discover a comet visible only through a telescope, for which she was awarded a gold medal from the King of Denmark. Later, Matthew Vassar recruited Maria as the first professor hired when Vassar College opened in 1865. Her arrival marked the start of a 150-year-long tradition of Vassar professors challenging students to learn by doing. This exhibit highlights research efforts by Maria and her students to record and study the Sun.

They first began recording sunspots by eye in 1868, just a few years after the College opened. Long before the days of Kodak and Polaroid, Maria ventured into the new world of astrophotography by pouring hand-prepared emulsions over glass plates to record astronomical events more precisely than the eye could see. By 1873, Maria began taking daily photographs of the Sun. Using the College’s 12” refractor, whose mahogany and brass casing now resides in the Smithsonian’s National Museum of American History, Maria projected images of the Sun onto the photographic plates using an apparatus she constructed. She surmised that sunspots were not just clouds on the surface of the Sun, as astronomers had thought, but were whirling cavities. In 1997, 200 photographic plates were re-discovered in a closet of the old Vassar College Observatory (now renamed the Maria Mitchell Observatory and designated a National Historic Landmark), still in their original envelopes complete with hand-written observational notes by Maria and her students. Although many of the plates are in poor condition through deterioration with age, they provide fascinating insights into astronomy in the late 1800s.

To put Maria’s world of astronomy in context, the period of the 1870s was a half-century before several fundamental discoveries. Not till well into the 20th century did astronomers confirm that there were other galaxies besides our own Milky Way galaxy, realize that stars shine because of energy emitted during nucleosynthesis when hydrogen fuses into helium in star cores, and understand that the absorption lines in the spectra of stars and star colors were an indication of their surface temperatures. (Maria once remarked, “I am just learning to notice the different colors of the stars, and already begin to have a new enjoyment.” She thought that the colors had to do with different chemical compositions.) Astronomical research in Maria’s period largely involved studying astronomical orbits such as stars in binary systems, comets and asteroids in the Solar System, and moons of planets, and making observations of changes in variable stars’ brightnesses and markings on planets or the Sun. Maria pursued research in all of these areas, and was one of the first to speculate that Jupiter’s bands were the result of storm systems.

Maria led by example, keeping students up past their curfew as they pursued astronomical objects till they sank to the tree-lined horizon in the pre-dawn hours (she once famously asked the campus gardener to trim tree limbs – and eventually the whole tree – so she could continue her observations at low elevation). She escorted students on cross-country trips to view solar eclipses in Iowa in 1869 and in Colorado in 1878. Maria recorded in her journal at the time of the Colorado eclipse, “As the last rays of sunlight disappeared, the corona burst out all around the sun, so intensely bright near the sun that the eye could scarcely bear it; extending less dazzlingly bright around the sun for the space of about half the sun’s diameter, and in some directions sending off streamers for millions of miles…It was now quick work. Each observer at the telescopes gave a furtive glance at the un-sunlike sun, moved the dark eye-piece from the instrument, replaced it by a more powerful white glass, and prepared to see all that could be seen in two minutes forty seconds. They must note the shape of the corona, its color, its seeming substance…” (Maria Mitchell: Life, Letters, and Journals, compiled by her sister Phebe Mitchell).

Some of the plates in this exhibit have envelopes bearing the writing of Mary Whitney, one of the 6 students known as “the hexagon” in Maria’s first class. Maria was known as a taskmaster but also much admired and appreciated by the students. She lived at the Observatory (along with her father for many years) and entertained students in her living room directly outside of the dome. She instituted a tradition of hosting a party at the end of each academic year, in which everyone read astronomical poems that they composed. These Dome Parties continue today at Vassar at the close of each semester.

Mary Whitney succeeded Maria as Director of the Observatory. Mary was a prolific writer and published over 100 astronomical papers. Several of Mary’s students became prominent astronomers as well. Notable Vassar astronomy alumnae from the late 1800s and early 1900s besides Mary Whitney include Antonia Maury, Margaretta Palmer, Christine Ladd-Franklin, and Caroline Furness. American women in the late 1800s had limited options to pursue astronomy. Most came from Vassar or Wellesley and either stayed at their institution or worked as research assistants at Yale or Harvard or Columbia. These female “human computers” were well regarded for their patience and persistence in tedious work, such as cataloging and categorizing observations of variable stars and stellar spectra. These painstaking observations led to several important discoveries that are fundamental to stellar astronomy today.

Maria noted that “The eye that directs a needle in the delicate meshes of embroidery will equally well bisect a star with the spider web of the micrometer.” She describes in her diary using real spider web threads to provide a precise narrow line with which to mark the exact position of a star or comet while noting the time of the night. The old Observatory, which now houses the Education Department, has an entryway filled with quotes by Maria Mitchell and photographs of her with her students.

Orbit calculations were a routine part of Maria’s mathematical astronomy courses that were required of all Vassar students. Astronomers understood orbits well enough to know that Venus and Mercury sometimes transit the Sun. In fact, Maria calculated the orbit of Venus as a paid employee for the United States Nautical Almanac. As these inner planets cross the Sun’s surface, they show up as tiny black dots. Several of Maria’s plates on exhibit show these rare events. In one case, she marked the projected path of Mercury across the Sun’s surface. In another, she viewed the transit of Venus with the Sun low in the sky, and partially obscuring trees near the Observatory provide a spider web appearance across the plate. The transit of Venus was a rare occurrence; transits occur in pairs separated by eight years and then repeat after more than 100 years. After the transit Maria observed in 1882, the next transit was in 2012, recorded at the Vassar Class of ’51 Observatory by the current Director of the Observatory, Professor Frederick Chromey, and students. Except for the path of Venus across the disk of the Sun, the modern-day photograph and Maria’s photograph are very similar.

Maria once said, “We especially need imagination in science. It is not all mathematics, nor all logic, but is somewhat beauty and poetry.” She would undoubtedly find the library exhibit of her work a fitting tribute to her efforts and her legacy at Vassar.