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300 BCE
Eratosthenes
When most people believed the world was flat, the notable Greek mathematician, astronomer and geographer Eratosthenes (276–195 B.C.) used the sun to measure the size of the round Earth. His measurement of 24,660 miles (39,690 kilometers) was only 211 miles (340 km) off the true measurement. He invented a system of longitude and latitude and made a map of the known world which could help others find measurements of other planets and stars. -
150 BCE
Claudius Ptolemy
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. According to NASA, "Ptolemy represents the epitome of knowledge of Grecian astronomy." It helped us get a good idea of the solar system even though it was wrong so we could find the right one. -
Period: 1508 to 1514
Nicolaus Copernicus
He proposed a model of the solar system that involved the Earth revolving around the sun. 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. -
Tycho Brahe
He discovered planets traveled around the sun not in circles but in ellipses. In so doing, he calculated three laws involving the motions of planets that astronomers still use in calculations today. However, closed minds put Kepler's work at risk. -
Johannes Kepler
With Tycho Brahe they determined that planets traveled around the sun not in circles but in ellipses. In so doing, he calculated three laws involving the motions of planets that astronomers still use in calculations today. However, closed minds put Kepler's work at risk. He seized its importance and were able to learn even more about the ways of the world and the heavens beyond. Also Keplers law. -
Sir Isaac Newton
He is most famous for his work on forces, specifically gravity. Building on the work of those who had gone before him — he is quoted as saying, "If I have seen further, it is by standing upon the shoulders of giants" — he calculated three laws describing the motion of forces between objects, known today as Newton's laws. This is important because Newton helped create a new, specialized form of mathematics. -
Albert Einstein
Einstein proposed 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. They led to the big-bang theory of how the universe was born.