Henrietta Swan Leavitt

She is an astronomer, October:

Henrietta Swan Leavitt

1868-1921

Member of the group of star trackers at Harvard Observatory, Leavitt discovered the period-luminosity relation, a novel method to measure the distance to astronomical objects. Leavitt found this relation after a systematic and detailed analysis of Cepheid stars. During one year (1905), she discovered 843 new variable stars in the Small Magellanic Cloud, discovering a total 2400 variables in this galaxy during her career. She also found four novae. The recognition of the importance of her scientific work came only after her death, partly because of the intention to nominate her for the 1925 Nobel prize, which was impossible as the prize can not be awarded post-mortem.

Despite her contributions to astronomy, when she died her professional standing was still at the assistant level.

Her work allowed astronomers to determine the size of our Galaxy and the scale of the Universe.

On the calendar there's also an old portrait photograph and an artist's impression of Henrietta studying photographic images.

More information from A Science Odyssey at PBS Online: she became head of the photographic photometry department at Harvard College Observatory, and developed the standard of photographic measurements known as the Harvard Standard.