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190 BCE
Eratosthenes
In 190 BC 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. This is important because people used to think that the Earth was flat so he was trying to prove that wrong. -
145
Claudius Ptolemy
In about 145 AD, In ancient Greece, astronomer and mathematician Claudius Ptolemy (A.D. 90–168) 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. This is important because we know more about the solar system and how it works. -
1570
Nicolaus Copernicus
In 16th century Poland, astronomer Nicolaus Copernicus (1473–1543) proposed a model of the solar system that involved the Earth revolving around the sun. This discovery is important because we found out that Earth is revolving around the sun so we learned more of of that. -
1576
Tycho Brahe
In 1576 Tycho Brahe helped overturn that belief in favor of a heliocentric model of the universe, with the sun at the center. This discovery is considered important because we have a better understanding of the universe. -
Johannes Kepler
In 1599 Johannes Kepler (1571–1630) 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. This is important because to know because we are able to calculate things easier. -
Sir Isaac Newton
In about 1680 English astronomer Sir Isaac Newton (1643–1727) 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 it gives us more information on gravity. -
Albert Einstein
In the early 20th century 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. This was an important discovery because we knew what time is like in space now.