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300 BCE
Discovered that the World Was Round (Eratosthenes)
The notable Greek mathematician, astronomer, and geographer Eratosthenes discovered that the world was round by using the sun to measure the size of the round Earth. His measurement of 24,660 miles was only 212 miles off the true measurement. This discovery is important because before this, most people believed that the world was flat. -
150 BCE
All Revolve Around Earth (Claudius Ptolemy)
The ancient Greek astronomer and mathematician 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. This system remained in place for hundreds of years, though it turned out to be wrong. This discovery is important because even though it was proved wrong in the future, it was one of the first models of the solar system. -
1500
Earth Revolves Around the Sun (Nicolaus Copernicus)
In Poland, astronomer Nicolaus Copernicus proposed a model of the solar system that involved the Earth revolving around the sun. The model was not completely correct, as astronomers of the time struggled with the backwards path Mars sometimes took. This discovery is important because it eventually changed the way many scientists viewed the solar system. -
1501
Earth Centered Model of the Universe (Tycho Brahe)
Tycho Brahe believed deeply in the Earth centered model of the universe. For thirty years he worked to prove it with very careful observations. This discovery is important because his observations were the greatest and the most accurate done with the naked eye, and because his data was eventually used by Johannes Kepler to devise his laws of planetary motion. -
Planets Travel in Ellipses (Johannes 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 but in ellipses. This discovery is important because in doing so, he came up with three laws involving the motions of planets that astronomers still use in calculations today. -
Basic Laws of Motion (Sir Isaac Newton)
Sir Isaac Newton formulated the basic laws of motion that are the basis of mechanics. These laws explained why Johannes Kepler's laws of planetary motion are true. He also expressed gravitation as a universal mathematical law and created calculus. This discovery is important because the laws represent mankind's first great success at describing diverse aspects of nature with simple mathematical formulas, and because they lay the groundwork for later physics developments. -
A New Way of Looking at the Universe (Albert Einstein)
German physicist Albert Einstein proposed a new way of looking at the universe that went beyond the current understanding. Albert 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 by an entity known as space-time, which is distorted by gravity. This discovery is important because Albert Einstein was expanding man's view of the universe.
