2018 Theme for the Event

Reaching for the Stars - Celebrating Astronomical Discoveries of Women Astronomers

Noether’s theorem (centennial)

On any list of history’s great mathematicians who were ignored or underappreciated simply because they were women, you’ll find the name of Emmy Noether. Despite the barricades erected by 19th century antediluvian attitudes, she managed to establish herself as one of Germany’s premier mathematicians. She made significant contributions to various math specialties, including advanced forms of algebra. And in 1918, she published a theorem that provided the foundation for 20th century physicists’ understanding of reality. She showed that symmetries in nature implied the conservation laws that physicists had discovered without really understanding.

Joule’s conservation of energy, it turns out, is a requirement of time symmetry — the fact that no point in time differs from any other. Similarly, conservation of momentum is required if space is symmetric, that is, moving to a different point in space changes nothing about anything else. And if all directions in space are similarly equivalent — rotational symmetry — then the law of conservation of angular momentum is assured and figure skating remains a legitimate Olympic sport. Decades after she died in 1935, physicists are still attempting to exploit Noether’s insight to gain a deeper understanding of the symmetries underlying the laws of the cosmos. On any decent list of history’s great mathematicians, regardless of sex or anything else, you’ll find the name of Emmy Noether.

Henrietta Swan Leavitt (150th birthday)

Born in Massachusetts on July 4, 1868, Henrietta Swan Leavitt attended Oberlin College in Ohio and then Radcliffe College, where she studied astronomy. Her excellent academic record impressed Edward Pickering, the director of the Harvard Observatory, where she volunteered to be a research assistant and soon earned a permanent job. She worked on mapping stars with the latest photographic and spectroscopic methods, eventually measuring the brightnesses of thousands of stars. Some of those stars varied in brightness over time (one of them, Delta Cephei, gave such stars the name Cepheid variables). Leavitt analyzed these Cepheids more thoroughly than her predecessors and noticed that the stars’ brightness varied on a regular schedule that depended on their intrinsic brightness. Leavitt worked out the “period-luminosity relationship” in 1908, giving astronomers a powerful tool for measuring the distance to stars and other astronomical objects.

Distance to a Cepheid nearby could be determined by parallax, enabling the determination of its intrinsic brightness based on its brightening-dimming schedule. Then, using nearby Cepheids’ intrinsic brightness, the bright-dim period for a more distant Cepheid could be used to infer its intrinsic brightness. That made it possible to calculate the star’s distance. Leavitt’s work made much of the 20th century’s dramatic revision of humankind’s conception of the cosmos possible. “Her discovery of the period-luminosity relationship in Cepheid variable stars is absolutely fundamental in transforming people’s ideas about first, our own galactic system and second, providing the means to demonstrate that galaxies do in fact exist,” historian Robert Smith said in a talk last January.