Book Review: Miss Leavitt’s Stars

Miss Henrietta Swan Leavitt obtained work at Harvard Observatory to review photographic plates. These were coming in fast and furious from the many large observatories being built in the Americas. These plates recorded the moment, but humans needed to interpret the dots. Small differences may be due to atmospheric effects, telescope adjustments, emulsion reactions or human intervention. Yet interpreting dots was considered an unworthy task for men, so women like Miss Leavitt were paid about minimum wage to spend hours every day looking at these plates, comparing each against another and against various metrics. With their effort, characteristics were catalogued for tens of thousands of stars.

The biography of a human computer sounds dry without even cracking open a book’s cover. Their task would simply be onerous repetition of the mundane. However, Johnson puts little time describing this aspect of Leavitt’s life. Actually, as Johnson acknowledges, there’s precious little remaining that describes Leavitt at all. Almost no first hand records exist. Most documents are second hand in nature and regard her circumstances from a very business like view. For example, either the observatory director or another astronomer would write discussing Leavitt’s work, her results and interest for future work. Johnson even had to dig into census data to discover where she lived and with whom. With such a dearth of information, Johnson has had to expand upon writing a biography so he adds a good look at the venture directly related to Leavitt’s work, the estimation of the size of the universe.

As such, Johnson smoothly takes the reader on a journey through parallax measurements, red-blue shifting, luminosity, galaxies and variables. Certainly there’s Leavitt’s discovery published in 1908 where she noted that brighter variables have longer periods. This observation came in a publication that gave a full account of 1777 variables in the Magellanic Cloud, and was so entitled. We also read of Shapely’s and Curtis’s debate in 1920 on whether the Milky Way was the universe or whether the Milky Way was just one typical galaxy amongst others. Eventually Edwin Hubble used Leavitt’s relationship of Cepheid variables to show that Barnard’s Galaxy was over 700 000 light years away and certainly outside the realm of the Milky Way. Johnson then ends the book with a discussion of Hubble’s constant that relates a galaxy’s velocity to its distance.

As one can tell, this book is much more than just about Leavitt. There’s some mention of her childhood, her accommodations and relatives. There’s also some information about her vacation travels, her frequent time off for convalescence and the on-set of her deafness. Johnson does add nice touches about society at the time, such as Leavitt completing the requirements for a Bachelor of Arts degree, but because she wasn’t male, she could only get a certificate. He also notes the better known information, such as her epic in 1914 on the North Polar Sequence, which at 84 pages defined 96 stars for use as a standard for all astronomers. But as most of this could have been done in a small number of pages, Johnson ably and expansively enlarges this biography to include the topic that so dominated Leavitt’s work.

Therefore, though the title may be a bit misleading, this book does an admirable job at presenting Leavitt’s life and especially her life’s interest. As well, Johnson wrote all astronomical details from a generalist’s point of view which can easily be understood by anyone without training. Corollaries are common and clear. The occasional wandering in the subject adds to the reading rather than distracts the reader. The few pictures help visualize the main characters, while the adherence to the subject keeps the book tight and informative.

Computers will do what they’re told. But they can’t step back and deduce patterns nor generalize. Humans excel at this function and George Johnson in his book, Miss Leavitt’s Stars, presents the benefit all astronomers owe to Miss Henrietta Swan Leavitt, the human computer who first came to understand the relationship between the periodicity of Cepheid variables and their distance. His book shows she was a special person who admirably worked above the call of duty to augment our knowledge one step further.

Review by Mark Mortimer

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