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Period: 276 BCE to 195 BCE
Eratosthenes
Eratosthenes used the sun to measure the size of the round Earth (at the time many believed the Earth was flat). He came up with a measurement of 24,660 miles which was only 211 miles off of the actual measurement. -
Period: 100 to 170
Claudius Ptolemy
Ptolemy discovered that starlight is refracted in the Earth's atmosphere. Sadly, he also invented the theory that the Earth is in the center of the universe. -
1514
Nicolaus Copernicus
Nicolaus proposed that the center of the universe was not Earth, but rather that the sun was near the center. He suggested that Earth's rotation was the reason for the rise and set of the Sun. He also correctly proposed that the Earth's movement through space caused the motion of the planets across the night sky. -
1577
Tycho Brahe
Tycho observed a comet, which at the time was consider a disturbance in the atmosphere, but Brahe's measurements proved that the comet orbited beyond the path of the moon. -
Johannes Kepler
Kepler studied the work of Nicolaus Copernicus. Kepler defended Copernicus theory that planets orbited the Sun rather than Earth. Kepler further proved this theory with Kepler's laws: 1. Planets travel on elliptical paths 2. An invisible line connecting the sun to a planet covered the same amount of area over the same amount of time 3. The relationship between the period of two planets is connected to their distance from the Sun (note: the 3rd law was published a decade after the others) -
Sir Isaac Newton
Newton published Newton's laws of motion for the universe: 1. Objects move at the same velocity unless another object caused a change. 2. Force acting on an object is equal to the object's mass times it's acceleration. 3. For every action in nature, there is an equal and opposite reaction. It was from these laws that Newton calculated the universal law of gravity. -
Albert Einstein
Einstein showed physical laws are identical for all observers, as long as they are not under acceleration. He proved that the speed of light in a vacuum is always the same, regardless at what speed the observer is traveling. This led scientists to realize that space and time are linked.