Western Slope Skies 7/19/13

Jul 19, 2013

This is the second in a series on Women in Astronomy. 

In the early 1900s, Henrietta Swan Leavitt discovered a characteristic of certain variable stars that is still used today to measure astronomical distance. 

Henrietta Leavitt was born on the Fourth of July, 1868.  She graduated from what is now Radcliffe College and took her first course in astronomy as a senior. Her first job was a photographic plate analyst for Edward Pickering at the Harvard Observatory. Pickering called these analysts ‘computers’.  They were all women. 

According to Pickering, they were better than men, because they were meticulous, accurate, and, to be honest, lower cost.  Leavitt worked for 25 cents per hour for a 42 hour week.  This equates to about $260 per week in today’s dollars.                                                                                    

Leavitt studied variable stars, which change brightness with time.  After cataloging thousands of variable stars, Leavitt noticed that certain variables were brighter if they had a longer period.  Although Leavitt did not use the term, this group became known as Cepheid variables, after Delta Cephei, one of the earliest identified variable stars.

Leavitt published papers in 1908 and 1912 confirming the relationship between brightness and period of Cepheid variables.  This established Cepheids as standard candles that can be used to estimate distances. If you know the period, which can be observed, then you can estimate the brightness.  In combination with other data, this brightness allows us to calculate distance.

Leavitt died in 1921.  Edwin Hubble often said that Leavitt deserved the Nobel Prize. A member of the Swedish Academy of Sciences considered nominating Leavitt, only to learn that she had died. If she had lived and been awarded the prize, she would have been only the second woman at that time to receive a scientific Nobel Prize.

Colleagues of Leavitt at the Harvard Observatory who also made important contributions to astronomy include Annie Cannon, Antonia Maury, and Williamina Fleming.

If you are interested in learning more about Henrietta Leavitt, read “Miss Leavitt’s Stars” by George Johnson.  The Montrose Library has a copy.