Much of what we know about the scale of the universe rests on a method worked out by a woman employed as a human computer at Harvard for a few cents an hour

Key Points:

• Henrietta Swan Leavitt, working as a human computer at Harvard College Observatory, discovered the period-luminosity relation for Cepheid variable stars, enabling astronomers to measure distances to faraway galaxies.
• Leavitt's discovery provided a crucial rung on the cosmic distance ladder, allowing astronomers to estimate distances beyond the reach of parallax methods by relating a Cepheid's pulsation period to its true brightness.
• Although Leavitt was not credited fully during her lifetime and was barred from calibrating her own findings, her work was foundational for Edwin Hubble's discovery that galaxies like Andromeda lie outside the Milky Way, vastly expanding the known universe.
• Leavitt's period-luminosity relation, now called Leavitt's Law, remains central to modern cosmology, underpinning measurements of the universe's expansion rate and contributing to Nobel-winning research on cosmic acceleration.
• Contemporary researchers continue to refine Leavitt's original data and methods due to ongoing discrepancies in measured expansion rates of the universe, highlighting the lasting importance of her early 20th-century work.