Henrietta Swan Leavitt

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Lore & Background

Henrietta Swan Leavitt discovered in 1908 the strong direct relationship between a classical Cepheid variable's luminosity and pulsation period. This relationship was used by Edwin Hubble for scaling galactic and extragalactic distances. Hubble proved that many objects previously thought to be nebulae were actually galaxies beyond the Milky Way by identifying Cepheid variables in the Andromeda Nebula and Triangulum Nebula, using Leavitt's Law to calculate their distances. Hubble's 1929 confirmation that a galaxy's recessional velocity increases with its distance from Earth, known as Hubble's law, also relied on distance measurements made possible by Leavitt's discovery. The Hubble Space Telescope was named in honor of Edwin Hubble.

Reader's Guide

Leavitt's Law, the period-luminosity relationship for Cepheid variables, became the essential tool for measuring cosmic distances. Edwin Hubble used it in 1924 to identify Cepheids in several nebulae, including the Andromeda Nebula and Triangulum Nebula. His observations proved these objects were entire galaxies far beyond the Milky Way, settling the debate about the universe's scale. Hubble later combined Leavitt's Law with redshift measurements from Vesto Slipher and Milton L. Humason to establish Hubble's law in 1929, showing the universe is expanding. Without Leavitt's discovery, Hubble could not have made these fundamental breakthroughs in extragalactic astronomy and observational cosmology.

Did You Know?

• Henrietta Swan Leavitt discovered the period-luminosity relationship for Cepheid variables in 1908.
• Edwin Hubble used Leavitt's Law to prove that the Andromeda Nebula and Triangulum Nebula were galaxies beyond the Milky Way.
• Hubble's 1929 discovery of the relationship between recessional velocity and distance relied on distance measurements made possible by Leavitt's work.
• Leavitt's discovery provided the first standard candle for measuring distances to other galaxies.