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Period: 276 BCE to 195 BCE
Eratosthenes
He used the sun to measure the size of the round Earth, according to NASA. His measurement of 24,660 miles (39,690 kilometers) was only 211 miles (340 km) off the true measurement. -
Period: 90 to 168
Claudius Ptolemy
He set up a model of the solar system in which the sun, stars, and other planets revolved around Earth. Known as the Ptolemaic system, it remained in place for hundreds of years, though it turned out to be flat wrong. -
Period: 1473 to 1543
Nicolaus Copernicus
He proposed a model of the solar system that involved the Earth revolving around the sun, according to NASA. The model wasn't completely correct, as astronomers of the time struggled with the backwards path Mars sometimes took, but it eventually changed the way many scientists viewed the solar system. -
Period: 1571 to
Tycho and Kepler
Using detailed measurements of the path of planets kept by Danish astronomer Tycho Brahe, Johannes Kepler determined that planets traveled around the sun not in circles, as Copernicus had thought, but in ellipses. In so doing, he calculated three laws involving the motions of planets that astronomers still used today. Kepler defended and modified the Copernican view of the solar system with a radical reformation that established him as one of the great lights of the Scientific Revolution -
Period: to
Newton
The well-known Newtonian laws of motion are: 1) an object at rest tends to stay at rest and an object in uniform motion tends to stay in uniform motion unless acted upon by a net external force. 2) The net force on an object is equal to the rate of change of its linear momentum. 3) For every action there is an equal and opposite action. Newton supposedly found inspiration for his theory of gravitation upon seeing an apple fall from a tree. -
Period: to
Einstein
became one of the most famous scientists ever after proposing a new way of looking at the universe that went beyond current understanding. Einstein suggested that the laws of physics are the same throughout the universe, that the speed of light in a vacuum is constant, and that space and time are linked in an entity known as space-time, which is distorted by gravity.