2500 BC
  Stonehenge is used to predict eclipses of the Moon.
1800 - 400 BC
  The Babylonians develop the first calendar based on the motion of the Sun and the phases of the Moon.
165 BC
  Chinese astronomers record the first sunspots.
46 BC
  The Julian calendar is brought into use in the Roman Empire by Julius Caesar.
635 AD
  A Chinese scholar discovers that the tail of a comet always points away from the Sun.
1054 AD
  Chinese astronomers witness the supernova explosion that creates the Crab nebula.
1066 AD
  A large comet, now known as Halley's Comet, is first seen.
1350 AD
  Jean Buridan develops the idea of "impetus," now known as inertia.
1500s AD
  The first reflecting telescope is developed by Leonard Digges.
1519 AD
  Ferdinand Magellan describes the Magellanic Clouds in detail.
1543 AD
  Copernicus is the first to place the Sun at the center of the universe.
1550 AD
  Leonard Digges makes the first refracting telescope.
1572 AD
  Tycho Brahe observes a supernova.
1576 AD
  Thomas Digges discovers that the stars are distributed into an endless infinity of space.
1582 AD
  The Gregorian calendar, the calendar used today, is introduced by Pope Gregory XIII.
1590 AD
  Mira becomes the first star to be discovered by David Fabricus, a Dutch astronomer.
1596 AD
  Tycho Brahe completes the best star catalogue of pre-telescopic times.