Ancient Astronomers Timeline

Eratosthenes

240 BCE

Greek mathematician, astronomer and geographer Eratosthenes used the sun to measure the size of the round Earth, according to NASA. This is important because he was able to do it with incredible accuracy and he was able to make a catalog of 675 stars. 195-276 B.C.

Claudius Ptolemy

127 BCE

Claudius Ptolemy published the Almagest, a comprehensive treatise on the movements of the stars and planets. This is important because it expanded Hipparchus’ geometric model of celestial motions, utilizing epicycles and eccentric circles in a geocentric theory which placed the Earth at the center of the solar system. This presented tables of information allowing convenient predictions of planetary locations. He also catalogued 48 constellations, which are still in use at present. 90–168

Nicolaus Copernicus

1504

Nicolaus Copernicus proposed a model of the solar system that involved the Earth revolving around the sun, according to NASA. This discovery is considered important because it eventually changed the way that many scientists viewed the solar system. 1473–1543

Tycho Brahe

1572

He made the most accurate celestial observations of his time and challenged the prevailing belief in how the universe was organized. This was a tremendous feat before the invention of the telescope. His aim was to confirm his own picture of the universe, which was that the Earth was at rest, the sun went around the Earth and the planets all went around the sun. Born in Denmark in 1546
Died in 1601

Johannes Kepler

1605

Johannes used the path of planets kept by Danish astronomer Tycho Brahe. He made the discovery that planets traveled around the sun not in circles, as Copernicus had thought, but in ellipses. This is important because he calculated three laws involving the motions of planets that astronomers still use in calculations today. 1571–1630

Sir Isaac Newton

1686

He is most famous for his work on forces, mostly gravity. His discoveries were that he calculated three laws describing the motion of forces between objects, known today as Newton's laws. This is important because his discoveries were the most influential figure in all of science. He invented calculus, as well as investigating optics, mechanics, experimental chemistry, alchemy, and theology. 1643–1727

Albert Einstein

1905

Albert Einstein discovered that the laws of physics are the same throughout the universe and that the speed of light in a vacuum is constant, and that space and time are linked in an entity known as space-time. This is important because this proposed a new way of looking at the universe that went beyond current understanding. 1879–1955