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400 BCE
Eudoxus
Eudoxus explains retrograde motion. Eudoxus' explanation involved the rotation of spheres in opposite directions. This geocentric model had the Earth at its center. -
350 BCE
Aristotle
Aristotle argues celestial bodies are spheres. Aristotle used a number of proofs that the Earth is a sphere, including the observation that its shadow on the Moon during lunar eclipses is always a circle -
250 BCE
Eratosthenes
Eratosthenes finds circumference of Earth. Eratosthenes uses observations of the altitude of the Sun to find the circumference of the Earth. His estimate may have been accurate to within a few percent -
1473
Copernicus (Dark Ages)
Nicolaus Copernicus Proposed the idea of the heliocentric universe, or the idea that the sun is the center of the universe and the Earth revolves around it. Proclaimed that the earth is only the center of gravity and center of the moon's orbit -
1571
Johannes Kepler
Johannes Kepler Created laws of planetary motion, He was the first to explain the principles of how a telescope works, Suggested that the Sun rotates about its axis in "Astronomia Nova" -
Hans Lippershey
Hans Lippershey was credited for the creation of the telescope -
Galileo
Galileo uses telescope for astronomical observations. Galileo didn't invent the telescope but he was among the first to use a telescope to examine the heavens. He carried out important observations of the Sun, Moon, Planets, and Stars -
Christain Huygens
Christian Huygens proposes that light consists of waves. Huygens' ideas were disputed by Newton, who proposed that light was made up of a stream of particles -
Edmund
Edmund Halley predicts return of Comet Halley. Halley noted that comets with similar orbits had appeared in 1456, 1531, 1607, and 1682. He proposed that these were all the same comet and that it would return in 1758 or 1759 - which it did -
William Herschel
William Herschel uses star counts to map Milky Way. Herschel assumed that the galaxy extended farther in directions in which he could see more stars. He found the galaxy to be flattened with the Sun near the middle -
Jan Ort
Jan ort proved the theory of the milky way galaxy having its own rotation axis. Found that the sun is 30,000 light years away from the center of the milky way galaxy. -
Karl Jansky
Karl Jansky Named the father of radio astronomy
Built and used antennas that picked up on radio frequencies of several things that caused static. He said that he got frequencies of the radiation from the sun. -
Carl Sagan
Carl Sagan Found that Venus atmosphere was very similar to Earth's
Discovered the seasonal changes from Mars.
