K.Botha - Timeline

Isaac Newton publishes "Principia Mathematica" which, among other things explains the law of universal gravitation

Georges Lemaitre proposes the Big Bang theory which states that the universe began from a single primordial atom

Edwin Hubble discovers evidence of an expanding universe which supports the Big Bang theory

Friedrich Bassel observes the stellar parallax - the apparent movement of the stars due to the Earth's orbit of the Sun

Arno Penzias and Robert Wilson discover cosmic microwave background radiation further supporting the Big Bang model

Ferdinand Magellan observes the Magellanic Clouds which are later recognised as galaxies outside the Milky Way

Kepler publishes "Astronomia Nova" which explains the motion of the planets using a heliocentric model of the universe and elliptical orbits

Thomas Wright suggests that the Milky Way galaxy is a flattened disk of stars and that nebulae might be other galaxies

William Herschel constructs the first map of the Milky Way

Ernst Opik demonstrates that the Andromeda nebula lies outside the Milky Way galaxy