Astronomy

By jlohmeyer6
  • 240 BCE

    Eratosthenes Measures Earth's circumference

    Using shadows and geometry, he produced a remarkably accurate estimate of Earth’s size.
  • 1543

    Copernicus publishes De Revolutionibus Orbium Coelestium

    Introduces the heliocentric model, proposing that Earth orbits the Sun.

  • Galileo uses a telescope for astronomy for the first time

    He discovers lunar craters, Jupiter’s moons, and the Milky Way’s star structure.

  • 1610 — Galileo discovers the four Galilean moons of Jupiter

    Io, Europa, Ganymede, and Callisto; helped prove not everything orbits Earth.

  • Isaac Newton publishes Principia Mathematica

    Defines universal gravitation and laws of motion, explaining planetary orbits.

  • William Herschel discovers Uranus

    The first planet discovered with a telescope.

  • Discovery of Neptune

    Mathematicians predicted its position before it was observed, proving gravitational modeling.

  • Einstein’s Special Theory of Relativity

    Revolutionizes understanding of space, time, and the speed of light.

  • Einstein predicts gravitational waves

    Not detected until a century later.

  • Edwin Hubble proves that “spiral nebulae” are galaxies

    Shows that the universe extends beyond the Milky Way.

  • Hubble discovers universe is expanding

    Galaxies are moving away from us; foundation of Big Bang theory.

  • Clyde Tombaugh discovers Pluto

    Later reclassified as a dwarf planet.

  • Yuri Gagarin becomes first human in space

    Major milestone in human spaceflight.

  • Apollo 11 Moon landing

    Neil Armstrong and Buzz Aldrin become the first humans on the Moon.

  • Voyager 1 & Voyager 2 launched

    Study outer planets; Voyager 1 becomes the first spacecraft in interstellar space.

  • Hubble Space Telescope launched

    Transforms modern astronomy with high-resolution space-based imaging.

  • First exoplanet orbiting a Sun-like star discovered

    51 Pegasi b confirmed; beginning of modern exoplanet science.

  • Pluto reclassified as a dwarf planet

    The International Astronomical Union (IAU) redefines “planet.”

  • Curiosity rover lands on Mars

    Begins detailed exploration of Mars’ geology and habitability.

  • New Horizons flies by Pluto

    First detailed images of Pluto and its moons.

  • First detection of gravitational waves

    LIGO confirms Einstein’s prediction from 1916.

  • James Webb Space Telescope (JWST) launched

    Begins returning detailed infrared images of galaxies, nebulae, and exoplanets.