Saturday, July 20, 2013

Miss Leavitt's Stars by George Johnson

The universe has grown a lot in the last century, at least in the estimation of astronomers. A series of observations, discoveries, and estimations have led from a view that the entirety of the universe is a smallish Milky Way galaxy to the present view in which many galaxies, and large clusters of galaxies, occupy a space that is billions of miles across.

One of the early, and still much used, discoveries that made measuring the universe possible was the period-luminosity relationship of a set of variable stars called Cepheids. Variable stars change in brightness over times. Cepheids change in brightness with a regular pattern. The length of that pattern, or period, is related to the average brightness of the star. Brightness and distance are hard to measure; the star appears brighter or dimmer based on how near or far away it is. Measuring the period of a Cepheid lets us know its brightness, and comparing that to its apparent brightness lets us know how far away it is (using a relationship called the inverse square law).

The Cepheid period-luminosity relationship was discovered by Henrietta Swan Leavitt. She was not recognized as a professional astronomer by the  academic leaders of Harvard University, where she worked, even though she had academic credentials and publications that put her on par with many who had doctorates in the field.

She was a woman and she was a computer. Before the invention of modern electronic computers, computers were people who managed data and performed calculations. Little is known about how Leavitt felt about the sexual discrimination that was common at the time, and she seemed to be contented with her life. Even so, if she had been a man, her accomplishments would very likely have earned her a plum appointment.

George Johnson’s book about this accomplished woman, Miss Leavitt’s Stars, is not a book about discrimination. It is a brief biography of a little-known astronomer who laid the groundwork for our understanding of the size of the universe.

Leavitt, who died relatively young, left a legacy in the science built on her work. Some of that appears in the work of famous Missourian Edwin Hubble, namesake of the Hubble Space Telescope, used Leavitt’s period-luminosity law to estimate the distance to Andromeda, and determine that it must be separate galaxy and not a cloud in the Milky Way. Astronomy has advanced a lot in the last 90 years, but astronomers continue to use Leavitt’s work to estimate distances in space when they can find Cepheids.

Johnson’s book is short. This is partly because Levitt didn’t leave much of a paper trail outside of her professional writing. It is about equal parts popular science and biography. I enjoyed it, yet I can imagine it being within the grasp of a high school student. It may be a good book for a budding astronomer or physicists. Unfortunately, there may not much more that we can learn about Leavitt, but her story is an introduction to Hubble, Einstein, and others who did important work relevant to astronomy.

Johnson, George. Miss Leavitt’s Stars: The Untold Story of the Woman Who Discovered How to Measure the UniverseNew York: Atlas, 2005.

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