People have described the stars, and named some of the brightest ones for thousands of years. Telescopes whose glass lenses gather and focus a star’s light make it easier to see, but could not explain a star’s color, or the sudden appearance of a bright new star (a “Nova”).
The invention of photography in the mid-1800s made accurate sky maps possible, if the photographer could carefully move his telescope to match the turning of the earth. Many universities built “observatories” with large telescopes that could do that.
Harvard University devised a way of preserving sky photographs by coating a glass plate with a thin layer of photo emulsion, then focusing the telescope on a bright star for a long time while the telescope and plate holder kept pace with the earth’s turning. The plate was then handled only by its edges and preserved in its own labeled envelope in a permanent file.
By carefully placing a new photo of that section of sky over it’s picture from a year ago, or ten or twenty years ago, tiny changes in position, brightness, color, etc. were detected in some of the several hundred stars on the plate. Focusing a star’s light on a spectroscope (like a glass prism separates sunlight into a rainbow of color) different stars had different results, together with black lines of various width and position that related to the star’s chemical composition.
Professor Edward Pickering, Harvard’s Observatory Director, attended a dinner in 1882, given by a wealthy couple interested in astronomy, who offered to finance the study of star’s spectra. With this funding, Pickering hired “computers”, clerks who would carefully study the photo plates to detect anomalies. A star that showed brightness and dimming on a regular cycle, might prove to be twin stars circling each other, bound by their mutual gravity, and regularly eclipsing each other. Analysis of a star’s spectrum could show the relative amounts of the various chemical elements it contained.
The book tells about individuals whose work led to discovering ways to measure a star’s distance from earth, it’s speed of movement, the source if its tremendous heat and light, its approximate age. Pickering’s housemaid, turned computer, Williamina Fleming proved to be an expert analyst, and spent most of her life analyzing spectra. Ann Cannon, a new graduate of Wellesley College, spent fifty years classifying several hundred thousand stars into a system internationally accepted in 1922, and still in use today.
Cecilia Payne was the first person to achieve a PhD in astronomy from Harvard for her method of of measuring the temperature of distant stars, and for estimating the great abundance of hydrogen in them, contrary to general belief of most astronomers of the time. In 1934, she met a young Russian refugee at an astronomy conference in Germany, suspected of being a Russian spy, yet denied re-entry into Russia under suspicion of being a German spy. She was able to get him entry into USA as a stateless person, and a job at Harvard as an astronomer. He and she worked together there for three months and then eloped to New York, returning to Boston as husband and wife. In 1956, she was promoted to full professor and chair of Harvard’s astronomy department.
The book takes longer to read because the author often switches back and forth between anecdotes of individuals, technical discussion about stars and galaxies, politics of Harvard and other universities, and history of the times, but can be very entertaining as well. A special section in the book briefly summarizes the life and accomplishments of fifty-three prominent astronomers over the past 150 years, and some of the observatories stationed around the world that enable good views of both northern and southern skies. It also contains a glossary of technical terms and a good index. And pictures of women who achieved their professional goals.
By coincidence, the British weekly news magazine Economist this week ( April 28th 2018) has an article in its science and technology section about the European Space Agency’s satellite Gaia, launched four years ago, whose computers have just downloaded a massive quantity of data about our home galaxy, the Milky Way. “Around 1.3 billion stars, perhaps about 1% of the Milky Way’s total have had their position, brightness, and motion measured accurately for the first time.” Astronomers had taken about 200 years to collect the first half-billion stars of the universe.