{ subscribe_url:'//blogs.loc.gov/share/sites/library-of-congress-blogs/inside_adams.php' }

Henrietta Leavitt, How She Loved the ‘Clouds’

Henrietta Swan Leavitt at about 30 years of age. Popular Astronomy, v. 30, no. 4, April 1922.

Henrietta Swan Leavitt (July 4, 1868-December 12, 1921) is not a name that’s familiar to most people.  Her name is certainly not as recognizable as Galileo, William Herschel, or Edwin Hubble, even though it ought to be.  I heard about Silent Sky, a play about her that’s opening at Ford’s Theater, which piqued my curiosity about this amazing woman.  Henrietta began her higher education at Oberlin College in Ohio before transferring to the Society for the Collegiate Instruction of Women, what is now Radcliffe University in Cambridge, Massachusetts.  While at the Society, Henrietta took a course in astronomy and was later an employee at the Harvard College Observatory where she performed stellar photometry under Edward Pickering.

While her time at the observatory was intermittent due to travel and illness, it was there, as a computer, that she thrived.  In her day-to-day tasks, Henrietta looked at photographic plates of stars to determine if their brightness had changed.  For those that had changed in brightness, or magnitude, she recorded the differences and over time determined their period.  These variable stars are known as Cepheid stars.  The plates that she looked at came from two observatories: the Harvard College Observatory and their outpost observatory in Arequipa, Peru.  The second allowed her to view the stars visible from the southern hemisphere, including the Magellanic Clouds.

Annie J. Cannon [and] Henrietta S. Leavitt [photograph]. Harvard University Archives.

These clouds, which are actually two dwarf galaxies that are visible in the southern hemisphere sky, are what Henrietta focused her attentions on while searching for variable stars.  In her landmark publication “1777 Variables in the Magellanic Clouds” she asserted that regarding these variable stars that the longer the cycle, the greater the brightness.  This period-luminosity relationship became known as Leavitt’s Law and though these words may not count for much, among astronomers it was a breakthrough (even though this work didn’t garner much attention upon release).  Her observations led to the Harvard Standard, which was a scale that measured the brightness of stars over 17 different magnitudes and was the standard to use when determining the magnitude of stars throughout the night sky.

Henrietta further locked in her law in her 1912 follow-up paper entitled “Periods of 25 Variable Stars in the Small Magellanic Cloud.”  In this paper, she called back to her previous publication: “In H.A. 60, No. 4, attention was called to the fact that the brighter variables have the longer periods, but at that time it was felt that the number was too small to warrant the drawing of general conclusions.  The periods of 8 additional variables which have been determined since that time, however, conform to the same law.”  This time, the astronomy community took note and began to use these variables as standards to determine distance in space to other stars that pulsated at the same rate using the inverse square law.

Henrietta Leavitt’s entry in the 1920 U.S. Census showing her occupation as “astronomer.”

For all her efforts, she was never known professionally as an astronomer, mainly due to her being a woman in very much a man’s world.  In the 1920 U.S. Census though, she did take a stand in having her occupation recorded as “astronomer.”  And there have been several posthumous honors such as having a crater on the far side of the moon, an asteroid, and a telescope named after her.  So the next time you look up at the stars on a clear night, just remember Henrietta made them just a bit clearer.

 

For more information regarding Henrietta Swan Leavitt and her field, check out these great books:

For more information on the Harvard Women Computers and their contribution to early 20th century astronomy, take a look at Project PHaEDRA.

And, for more information on women astronomers in general, consult the Women in Astronomy: A Comprehensive Bibliography by the Library of Congress.

The Perplexing Solar Corona and the Space Environment It Creates: Lecture with NASA’s Nicholeen Viall November 7

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. NASA Observatories examining the atmosphere of the Sun are revealing extraordinary detail in the solar corona. Material from this mysteriously super-hot outer layer expands outwards to become the solar wind, accelerating beyond the speed of sound and bathing […]

IT IS ROCKET SCIENCE! Exploring Earth’s Escaping Atmosphere with NASA’s Douglas Rowland on October 17

NASA’s Dr. Rowland will talk about atmospheric escape, his adventures in Norway, and what is being learned from the VISIONS-2 data in his lecture, Exploring Our Escaping Atmosphere: Going above the Top of the World to Watch the Sky, on Thursday, October 17, from 11:30 a.m.-12::30 p.m. in the Madison building’s third floor Pickford Theater.

The Enchantress of Number

This blog was written in preparation for Ada Lovelace Day, which occurs every year on the second Tuesday of October and celebrates women in STEM. Augusta Ada Byron, daughter of the famous poet Lord Byron and intellectual Lady Byron (whom Byron once named the “Princess of Parallelograms”), was born in 1815.  Shortly after Ada’s birth, […]

Peter Parley Explains the Moon to Children, Part 1

Today’s guest post is by Jacqueline Coleburn and Anthony Mullan. Jackie is a rare book cataloger at the Library of Congress and is cataloging the Library’s rare children’s books.  Peter Parley books are a particular interest of hers. These books, which were very popular in the 1830s, 40s, and 50s, offer insight into the evolution […]

The Parker Solar Probe, Mission to “Touch the Sun”: December 6 NASA Lecture with Dr. Alex Young

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. One of NASA’s most exciting missions, the Parker Solar Probe (PSP) launched from Cape Canaveral on August 12, 2018. The mission’s findings will help researchers improve forecasts of space weather events, which have the potential to damage satellites, […]

The ICESat Man Cometh: Lecture November 8 with NASA’s Tom Neumann

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. On November 8 the Library will welcome cryospheric scientist Tom Neumann, who will speak on “GRACE-FO and ICESat-2:  NASA’s Leadership in Monitoring the Polar Regions from Space.”  Dr. Neumann is deputy project scientist on ICESat-2 (Ice, Cloud, and […]

NASA Astrobiologist Melissa Trainer to Speak at the Library October 11 on Titan: An Exotic Ocean World Waiting to be Explored

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. Before the twenty years of the Cassini-Huygens mission, little was known about Saturn’s largest moon Titan, except that it was Mercury-sized and its surface was hidden beneath a thick, nitrogen-rich atmosphere. The Cassini mission mapped Titan’s surface, studied […]

Shadow Science: Using Eclipses to Shed New Light on Heavenly Bodies, September 12 Lecture with NASA’s Chief Scientist, Dr. James L. Green

This post was authored by Stephanie Marcus, Science Reference Librarian in the Science, Technology, and Business Division. People are still talking about the total solar eclipse of last August, and many of us are already excited about the next one on April 8, 2024.  That will be the only total solar eclipse in the 21st […]