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Ptolemy
Ptolemy wrote a history of previous observations called the "Almagest." He also performed many many experiments on optics and discovered that starlight is refracted in the Earth's atmosphere. He also developed the geocentric model (though it was incorrect) which was important because it produced sufficiently accurate predictions of planetary predictions. 100 AD - 170 AD. -
Copernicus
Copernicus was the first to challenge Ptolemy's geocentric model, instead explaining the heliocentric model, otherwise known as earth-centered. He also introduced the idea that day and night are the result of the rotation of the Earth on its axis and that Mercury and Venus are closer to the sun than the Earth is. This is important because his idea lead to the discovery that the Earth is not in fact the center of the universe, rather the sun is. 1473-1543. -
Tycho Brahe
Recorded planetary positions ten times more accurately than the best previous work. This was important because at the time, most people believed in the ideas of the geocentric model, but Brahe proved that the sun was the center of the universe. 1546-1601. -
Johannes Kepler
Kepler used Brahe's idea to develop the three laws that govern planetary motion. His major contribution was the idea that planets and other satellites move in elliptical orbits, not perfect circles, with the orbitted body as one focus. Armed with this theory, Kepler was able to predict the future positions of planets with much greater accuracy. 1571-1630. -
Eratosthenes
When most people believed the Earth was flat, Eratosthenes used the sun to measure the size of the round Earth. His measurement of 24,660 miles was only 211 miles off the true measurement. 276 BC - 194 BC. This is important because he proved that the Earth was round rather than flat. -
Isaac Newton
Newton formulated the basic laws of motion. He published these laws in his work, Philosophiae Naturalis Principia Mathematica. Newton's three laws are: an object at rest stays at rest, or an object in constant motion stays in constant motion, until it is acted upon by a force
the change in speed of an object is proportional to the force acting upon it when an object 1 exerts a force on object 2, object 2 exerts a force on object 1 equal and opposite to the original force. 1642-1727. -
Albert Einstein
Albert Einstein proposed a new way of looking at the universe that went beyond current understanding. He 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 is important because it helped us to understand how the universe worked better. 1879-1955.