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240 BCE
eratosthenes
Several astronomers and mathematicians before and after Eratosthenes tried to accurately measure the circumference of the Earth, but is was Eratosthenes that came through. He found the circumference of the Earth to be nearly 250,000 stadia (25,000 miles). His astronomical discovery help many astronomers know the accurately circumference of the Earth. -
Period: 127 to 41 BCE
Claudius Ptolemy
His Planetary Hypotheses went beyond the mathematical model of the Almagest to present a physical realization of the universe as a set of nested spheres, in which he used the epicycles of his planetary model to compute the dimensions of the universe. He believed that the Earth was the center of the Universe. The word for earth in Greek is geo, so we call this idea a "geocentric" theory -
1532
Nicolaus Copernicus
Nicolaus Copernicus discover Earth and the planets revolve around the sun led him to make a number of other major astronomical discoveries. And found that Earth takes one year to orbit the sun and during this time wobbles gradually on its axis, which accounts for the precession of the equinoxes. This discovery was very important because it would make him the first modern European scientist to propose that Earth and other planets revolve around the sun, or the Heliocentric Theory of the universe. -
Period: 1572 to 1577
Tycho Brahe
Tycho Brahe proved that comets were not just components of Earth's atmosphere, but actual objects traveling through space. Brahe showed irregularities in the Moon's orbit and discovered a new star in the Cassiopeia formation. Tycho Brahe discoveries are consider important because he made the most precise observations that had yet been made by devising the best instruments available before the invention of the telescope. -
Johannes Kelpler
Johannes discovered three major laws of planetary motion: (1) the planets move in elliptical orbits with the Sun at one focus; (2) the time necessary to traverse any arc of a planetary orbit is proportional to the area of the sector between the central body and that arc; and (3) there is an exact relationship between the squares of the planets’ periodic times and the cubes of the radii of their orbits. His discovery helped many astronomer know the three major laws of planetary motion. -
Sir Isaac Newton
He found that as two bodies move farther away from one another, the gravitational attraction between them decreases by the inverse of the square of the distance. He also solved the mysteries of light and optics, formulated the three laws of motion, and derived from them the law of universal gravitation. -
Period: to
Albert Einstein
Einstein's second 1905 paper proposed what is today called the special theory of relativity. This new theory stated that the laws of physics had to have the same form in any frame of reference. The theory also stated that the speed of light remained constant in all frames of reference. Later in 1905 Einstein showed how mass and energy were equivalent. Albert Einstein work continues to help astronomers study everything from gravitational waves to Mercury's orbit. -
Ancient Astronomers Timetoast Timeline Instructions
