What are stars? In the late 1800s, astronomers had a pretty good idea. Stars were clearly bright balls of gas, scattered throughout the Milky Way. In the 1830s, people had begun studying stars and measuring the distances to them. However, nobody was quite sure how stars formed, or what happened to them during their presumably long lives.
A Difficult Start to Studying Stars
Some stars appeared to come in pairs, but what this meant for those stars was unclear. Some odd stars seemed to vary in their brightness, and astronomers hadn’t yet managed to explain why. Another long-standing mystery concerned what stars were made of; researchers had observed signs of the same elements found on Earth, so most astronomers simply assumed that the stars shared roughly the same chemistry as our own planet.
We also had a serious problem: there were so many of them. How could we possibly study them all? There was no classification scheme for stars, and without an orderly approach, how could we ever learn more about how stars worked, or what they were made of?
Observations were also revealing that there were more than just stars to be studied; faint scraps of glowing gas, strange spiral nebulae, and tight clusters teeming with stars all suggested that there were many more astronomical mysteries hidden in the data that would need to be disentangled.
With heaps of data coming in from impressive new telescopes, and with relatively few professional astronomers on staff and limited funds even at the world’s best observatories, how could we possibly begin to address all these problems?
This article comes directly from content in the video series Great Heroes and Discoveries of Astronomy. Watch it now, on Wondrium.
Williamina Fleming: One Very Talented Housekeeper
Near the end of the 19th century, Edward Pickering, director of the Harvard College Observatory, was frustrated. He needed a large and skilled staff of assistants to analyze and classify the heaps of data being generated by the best telescopes of the day, and he was displeased with the work of the men in his employment known as ‘Computers’—people who did mathematical calculations.
Pickering’s housekeeper, Williamina Fleming, had worked as a teacher in Scotland and acquired a natural scientific curiosity from her father. Pickering’s wife, Elizabeth, recognized that Fleming’s talents extended beyond housework and encouraged her husband to hire her at Harvard.
Pickering was also a supporter of the idea that women could find work as scientists. It also helped that women could be hired for much lower wages than men, allowing him to employ a larger staff with the same funds.
Williamina Fleming soon became one of the founding members of the Harvard Computers, an all-female group that analyzed the cutting-edge telescope data of the day.
The Process of Developing Images
At the time, the best data from telescopes was quite literally cutting-edge: images were captured from telescopes on thin glass plates, treated on one side with chemical emulsions that reacted to light.
Carefully prepared plates would be loaded into a telescope’s camera in darkness and then exposed, with the emulsion darkening as light hit it to capture the data gathered by the telescope. After exposure, the plates were painstakingly developed and then carefully stored in envelopes, protected from light and moisture and even fingerprints, to be studied and analyzed later on.
Imaging: Two-dimensional Data of Stars
The astronomical data that these glass plates were gathering could be broadly sorted into two different categories: imaging and spectroscopy.
Imaging is precisely what it sounds like, two-dimensional data of stars or galaxies on a given night. These images could record the relative location of a star in the night sky, preserve how bright the star appeared to be on a given night, or capture the appearance of a glowing nebula.
In Pickering’s day, images were especially exciting when they captured the same stars night after night, carefully tracking the stars’ brightness to monitor how they changed over time. Astronomers at the time knew that some stars were variable and analyzing images of these stars from subsequent nights seemed key to studying how they changed with time.
Spectroscopy: What Stars Are Made Of
Spectroscopy, by contrast, doesn’t record a picture of an astronomical object. Instead, it preserves the colors of light that the star emits. In spectroscopic data, light from an object is split and sorted according to its color, or wavelength, by bouncing it through a prism or off of a microscopically ruled surface.
A telescope recording spectroscopic data would direct the bluest light, with the shortest wavelength, to one end of a photographic plate and the reddest light, with the longest wavelength, to the other, with intermediate wavelengths neatly sorted in the middle like a rainbow.
Splitting the light like this and measuring how much light we detect at each wavelength gives us an astronomical object’s spectrum. A spectrum is especially valuable because of what it can tell us about an object’s chemistry. Light absorbed or emitted by specific molecules or atoms has a very precise known wavelength.
A star with lots of hydrogen in its atmosphere, for example, would show a dark stripe in the yellowish region of the spectrum, where photons of that wavelength were being absorbed by hydrogen atoms. Another star with ionized calcium in its atmosphere would display a trio of dark lines in the red spectrum, and so on.
An expert spectroscopic analyst—like a Harvard Computer—could read the spectrum of a star, a bright streak interspersed with dark lines from absorbing elements, like a fingerprint.
Common Questions about Studying Stars in the Late 19th Century
Williamina Fleming, was a teacher prior to becoming Edward Pickering’s housekeeper. Her natural scientific curiosity and talents led to her being hired at Harvard. Also influential were the facts that Pickering believed in women becoming scientists and that women were paid lower wages than men.
Imaging was two-dimensional data of stars or galaxies on a given night. These images could record the relative location of a star in the night sky, preserve how bright the star appeared to be on a given night, or capture the appearance of a glowing nebula. Analyzing images of these stars from subsequent nights helped the astronomers learn how the stars changed with time.
In spectroscopic data, light from an object is split and sorted according to its color, or wavelength. Splitting the light like this and measuring how much light we detect at each wavelength gives us an astronomical object’s spectrum. A spectrum is especially valuable because of what it can tell us about an object’s chemistry.