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 Universe. New York: Atlas, 2005.
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