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Portrait of Henrietta Swan Leavitt

Science · Maths, astronomy, medicine & more

Henrietta Swan Leavitt

1868–1921 · American

Astronomy — variable stars

Henrietta Swan Leavitt was one of the women "computers" employed by Edward Pickering at Harvard College Observatory to study photographic plates. Examining variable stars in the Magellanic Clouds, she discovered that brighter Cepheid variables have longer periods, published in 1912. This period–luminosity relation, now called the Leavitt law, gave astronomers a "standard candle" for measuring cosmic distances and underpinned Hubble's work on galaxies and the expanding universe.

How to spot them

  • ▸Harvard computer under Edward Pickering; worked on photographic plates
  • ▸Cepheid variables in the Small Magellanic Cloud; the period–luminosity relation (Leavitt law)
  • ▸Discovered some 2,400 variable stars
  • ▸Profoundly deaf; died of cancer in 1921, before a planned Nobel nomination
  • ▸Subject of Lauren Gunderson's play Silent Sky

Key discoveries & works

Period–luminosity relation for Cepheid variables (1912)

Brighter Cepheids pulsate more slowly, so the period reveals true brightness and hence distance

1777 Variables in the Magellanic Clouds (1908)

Paper in the Annals of Harvard College Observatory first noting that brighter variables had longer periods

Periods of 25 Variable Stars in the Small Magellanic Cloud (1912)

Harvard College Observatory Circular 173, published under Pickering's name, setting out the relation

Discovery of about 2,400 variable stars (1900s–1910s)

Roughly half of all variable stars known at the time

North Polar Sequence of photographic magnitudes (1913)

A standard scale of stellar brightness on photographic plates, adopted internationally

Key ideas

  • Cepheid variables act as standard candles: measure the period, infer the luminosity, compare with apparent brightness to get distance
  • Because the Magellanic Cloud stars are all at about the same distance, differences in apparent brightness reflect real differences in luminosity
  • Her relation let Harlow Shapley size the Milky Way and Edwin Hubble show that Andromeda lies far beyond it

Quick-fire facts

  • •Born 4 July 1868 in Lancaster, Massachusetts; died 12 December 1921 in Cambridge, Massachusetts
  • •Studied at the Society for the Collegiate Instruction of Women, later Radcliffe College
  • •Began at Harvard College Observatory as a volunteer in the 1890s and was later paid a small wage
  • •The Swedish mathematician Gösta Mittag-Leffler wrote in the 1920s intending to nominate her for a Nobel Prize, unaware that she had died
  • •The relation is now formally called the Leavitt law
  • •Asteroid 5383 Leavitt and a lunar crater are named after her

Drill it — 6 cards

1 / 6new card

Sources