Charlotte Cynthia Barnum (May 17, 1860 – March 27, 1934), mathematician and social activist, was the first woman to receive a Ph.D. in mathematics from Yale University.
Charlotte was an editorial writer for Webster's International Dictionary from 1886 to 1890, and then taught astronomy at Smith College for the academic year 1889–90.
In 1890, Charlotte applied for graduate studies at Johns Hopkins University, but was turned down because they did not accept women.
She persisted and with the support of Simon Newcomb, professor of mathematics and astronomy at the university, she won approval to attend lectures without enrollment and without charge.
Starting in 1917, she worked in various organizations and academic institutions in Connecticut, New York and Massachusetts as an editor, actuary and teacher.