2 HENRIETTA LEAVITT BIOGRAPHY 980L HENRIETTA LEAVITT MEASURING DISTANCE IN THE UNIVERSE Born Died July 4, 1868 December 12, 1921 Lancaster, Massachusetts Cambridge, Massachusetts By Cynthia Stokes Brown, adapted by Newsela Henrietta Swan Leavitt studied distant stars that dim and brighten. These are called Cepheid variable stars. She made it possible for others to measure huge cosmic distances, discover additional galaxies, and begin mapping the Universe. 2 3 \Leavitt was a minister’s daughter. Her family moved frequently. period ranges from about one day to nearly four months. She attended the Society for Collegiate Instruction of Women, which is Leavitt studied thousands of photographs of these stars. She discovered now part of Harvard University. It was a school she had dreamed of a way to determine how bright they are and how far away they are. attending. In her senior year she discovered her calling — astronomy. She found that the longer a star’s period, the brighter it was. By comparing how bright a star appeared, and how bright it actually was, Leavitt could estimate how much of the star’s light had been lost while reaching Earth, At the Harvard College Observatory and how far away the star actually was. Leavitt liked astronomy so much that after graduation she became a volun- Leavitt published her first paper on the period-luminosity relationship in teer at the Harvard College Observatory as a “computer.” This was the 1908. Four years after that she published a table of the periods of 25 name used for women who examined tiny dots on photographs of the night Cepheid variables. Nine years later, in 1921, she died of cancer at age 53 sky. They then measured, calculated, and recorded their observations in in Cambridge, Massachusetts. ledger books. Eventually, Leavitt was hired at 30 cents an hour. She continued to work at the observatory for the remaining 19 years of her life. Leavitt’s Legacy Leavitt was very interested in the Magellanic Clouds, two glowing hazes in Before Leavitt established the period-luminosity relationship, astronomers space. At the time, no one knew what the clouds were. Since the Magellanic could only measure cosmic distances up to about 100 light years. Using Clouds are only visible in the southern hemisphere, Leavitt could not see her insights, astronomers were able to estimate the Magellanic Clouds to them directly. She could merely look at photographic plates taken at Harvard’s be about 100,000 light years from Earth — much further than anyone observatory in Peru, and sent to Cambridge by ship around the tip of South had imagined — meaning they could not be within the Milky Way galaxy. America. Edwin Hubble at the Mount Wilson Observatory near Los Angeles used a state-of-the-art telescope to find Cepheid variable stars that were extremely far away. They were so far away, they proved the existence of other galaxies. Using Cepheid variables By 1925, most astronomers agreed that our galaxy is just one of many. One of Leavitt’s jobs was to examine the variable stars, which, unlike most stars, vary in brightness because of changes within themselves. In the Leavitt initially worked under a director of the Harvard College Observatory course of her work, Leavitt discovered 2,400 new variable stars, half the who did not encourage theorizing but preferred only to accumulate data. known ones in her day. A later director even tried to take some of the credit for her work after her death. Now, however, Leavitt is recognized as a key contributor to our A certain group of variable stars, later called Cepheid variables, fluctuate understanding of the size of the Universe. in brightness (luminosity) in a regular pattern called their “period.” This 4 5 Timeline of Leavitt’s life 1902–1921 Paid work at Harvard College Observatory; gradually loses her hearing 1868 1893–1902 1902–1908 Born on July 4 Volunteer work Discovers 2400 Cepheid variable stars in Lancaster, MA at Harvard College and develops her period-luminosity theory Observatory 1888–1892 1908 Attends the Society for Publishes her theory on the correlation between Collegiate Instruction of period and luminosity in Cepheid variables Women (Radcliffe/Harvard) 1885–1888 1912 1921 Attends Oberlin College Publishes a table Dies of cancer on of 25 different Cepheid December 12 variable periods in Cambridge, MA 8 9 10 18701 2 3 4 5 6 7 8 9 10 18801 2 3 4 5 6 7 8 9 10 18901 2 3 4 5 6 7 8 9 10 19001 2 3 4 5 6 7 8 9 10 19101 2 3 4 5 6 7 8 9 10 19201 2 3 4 5 6 7 8 9 10 1876 1920 Telephone 1889 1898 Women in the patented Vincent van Gogh Marie Curie discovers United States gain paints Starry Night radium and polonium the right to vote 1870 1882 1916 Undersea cables connect Naturalist Charles Darwin Albert Einstein publishes his Europe, North America, and India dies in Kent, England General Theory of Relativity 1869 Dmitri Mendeleev devises 1914 the periodic table World War I begins During the time of Leavitt A modest life Leavitt never married. She gradually became deaf, starting with an illness when she was a young adult. She was buried in Cambridge in the family plot. Her total estate was appraised at $314.91. In her obituary, a senior colleague wrote: “[She] was possessed of a nature so full of sunshine that, to her, all of life became beautified and full of meaning.” 8 9 Image credits Henrietta Leavitt © Photo Researchers Articles leveled by Newsela have been adjusted along several dimensions of text complexity including sentence structure, vocabulary and organization. The number followed by L indicates the Lexile measure of the article. For more information on Lexile measures and how they correspond to grade levels: http://www.lexile.com/about-lexile/lexile-overview/ To learn more about Newsela, visit www.newsela.com/about. The Lexile® Framework for Reading The Lexile® Framework for Reading evaluates reading ability and text complexity on the same developmental scale. Unlike other measurement systems, the Lexile Framework determines reading ability based on actual assessments, rather than generalized age or grade levels. Recognized as the standard for matching readers with texts, tens of millions of students worldwide receive a Lexile measure that helps them find targeted readings from the more than 100 million articles, books and websites that have been measured. Lexile measures connect learners of all ages with resources at the right level of challenge and monitors their progress toward state and national proficiency standards. More information about the Lexile® Framework can be found at www.Lexile.com. 10 11.