Miss Leavitt’s Stars: The Untold Story of the Woman Who discovered How to Measure the Universe
By George Johnson
Atlas Books, 2005
One night at the observatory a voice in the dark asked “How do I reconcile the information that the Andromeda Galaxy is 2 million light years away with the growing number of scientists who agree that the Earth is only 6,000 years old?”
Two million light years away! Isn’t that remarkable? We are able to see and study something from such a tremendous distance! Thanks to Miss Henrietta Leavitt, we know how far lies this little smudge of 400 billion stars.
George Johnson presents a very readable and insightful tableau on which Leavitt’s work stands out, despite the paucity of primary sources.
Johnson takes us back into history reminding us that Hipparchus used an eclipse to calculate the distance to the Moon, and Renaissance astronomers used the transit of Venus to determine the length of an Astronomical Unit. John Hershel even used the motion of the solar system through the Milky Way to find the distance to Alpha Centauri.
But parallax has its limits, and the other side of the Milky Way was out of reach, no less those thousands of little smudges and spiral nebulae.
The drama of the Great Debate in 1920 is shared as part of the backdrop to the story. Herber Curtis gave evidence that the spiral nebulae were island universes while Harlow Shapley argued that the Milky Way was the universe. Both Curtis and Shapley thought they had prevailed.
Describing the Great Debate, Johnson writes
“…two of the world’s smartest astronomers could take the same trove of astronomical observations and come up with two such very different picture of the universe [is] a reminder that science lies not in the facts themselves but in their arrangement.”
The Miss Henrietta Leavitt, a computer at Harvard Observatory under the employ of Edward Pickering, noticed the period luminosity relationship of some of the stars she was classifying. Suddenly distances to the Small Magalenic Cloud and even M41 were within reach.
Following Leavitt’s untimely death in 1921 at age 53, the astronomical community struggled with itself to give her full credit for her discovery. In addition, questions arose about the possibility of different kinds of Cepheid stars, and about the effects of cosmic dust on observations.
It’s pretty clear to me that George Johnson stands on the side of Henrietta Leavitt and her discovery of the period-luminosity relationship. This is a good book and worth your time to read.
As for the questioning voice in the Observatory, the one raising the Creationist idea of a young Earth, I asked him to share the evidence.