Industrial AgeScience & Math Leavitt's period-luminosity law 1912Major Henrietta Swan Leavitt finds that brighter Cepheid stars pulse more slowly. Cepheids become a yardstick for distances to other galaxies. ▲ MattersSaveShareTrace roots Longest chain: The Big Bang → First stars ignite → Supernovae seed heavy elements → The Sun forms → Earth forms → First oceans → First life → Photosynthesis evolves → Great Oxidation Event → Complex cells (eukaryotes) → Multicellular life → First animals → Cambrian Explosion → First vertebrates → Jawed fish → Fish walk onto land → The amniotic egg → The Great Dying → Dinosaurs appear → Asteroid ends the dinosaurs → Early primates → Apes split from monkeys → Human line splits from chimpanzees → Walking upright → First stone tools → Genus Homo appears → Homo erectus → Control of fire → Habitual fire and cooking → Homo sapiens appears → Complex language → Natufian villages → Oldest known bread → Agriculture begins → Irrigation → Uruk and the first cities → Cylinder seals → Writing (cuneiform) → Babylonian mathematics → Babylonian astronomical diaries → Thales and natural philosophy → Trial and death of Socrates → Plato's Academy → Aristotle's Lyceum → Alexander's conquests → Death of Alexander and the Hellenistic kingdoms → Seleucid Empire founded → Parthian Empire founded → Sasanian Empire → Birth of Muhammad → Muhammad's first revelations → The Hijra → Conquest of Mecca → Death of Muhammad and the Rashidun caliphate → Arab conquests → Abbasid Caliphate → Battle of Talas → Paper reaches the Islamic world → House of Wisdom → Ibn al-Haytham's Book of Optics → Eyeglasses → Telescope → Galileo's telescope discoveries → Barometer → Boyle's law → Oxygen discovered → Lavoisier founds modern chemistry → First photograph → Leavitt's period-luminosity law Community notesLoading notes… Learn more ranked by votesBookGeorge JohnsonMiss Leavitt's Stars ↗Editor's pickBookDava SobelThe Glass Universe ↗Editor's pickVideoSearch on YouTubeHenrietta Leavitt Cepheid variables ↗Editor's pickVideoSearch on YouTubeperiod luminosity relation explained ↗Editor's pick