| Astronomer
| Contribution
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| HipparchusFor the Athenian tyrant, see Hipparchus (son of Pisistratus). Hipparchus ( Greek pi;παρχο&sigmaf (circa 190 BC circa 120 BC) was a Greek astronomer, astrologer, geographer, and mathematician. The ESA's Hipparcos Space Astrometry M and PtolemyThis article is about the geographer and astronomer Ptolemy. For Alexander the Great's general, see Ptolemy I of Egypt. For others, see Ptolemy (disambiguation). Claudius Ptolemaeus (Greek: Klaudios Ptolemaios; A. circa 85 circa 165), known in English as
| Determined the positions of about 1,000 bright stars, tried to explain the puzzles of astronomy without refuting the commonly believed geocentric model of universe and classified stars by magnitudeThe apparent magnitude m of a star, planet or other heavenly body is a measure of its apparent brightness; that is, the amount of light received from the object. Hundred times less bright (e. the same object ten times as far) corresponds to an apparent ma.
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| AristarchusAristarchus ( 310 BC circa 230 BC) was a Greek astronomer and mathematician, born in Samos, Greece. He is the first recorded person to propose a heliocentric model of the solar system, placing the Sun, not the Earth, at the center of the known universe (h
| First known person to propound the heliocentric modelIn astronomy, heliocentrism is the theory that the Sun is at the center of the Universe and/or the Solar System. The word is derived from the Greek Helios ("Sun"). Historically, heliocentrism is opposed to geocentrism and currently to modern geocentrism, of universe
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| Nicolaus CopernicusNicolaus (or Nicholas Copernicus (original name Kopernik or Koppernigk Polish Mikolaj Kopernik German Nikolaus Kopernikus February 19, 1473 May 24, 1543) was an astronomer, mathematician and an economist who developed a heliocentric ( Sun-centred) theory
| Reitererated the heliocentric model of universe.
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| Galileo GalileiGalileo Galilei ( Pisa, February 15, 1564 Arcetri, January 8, 1642), was a Tuscan astronomer, philosopher, and physicist who is closely associated with the scientific revolution. His great achievements include perfecting the telescope, a variety of astron
| Was the first to use the telescopeNice Observatory. A telescope is perhaps the most important astronomical tool; such technology gathers (and focuses) electromagnetic radiation. Telescopes increase the apparent angular size of objects, as well as their apparent brightness. Galileo Galilei to observe the sky. Condemned to house arrest for his discoveries by Inquisitional edict... which was lifted 359 years later by Pope John Paul II.
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| Johannes Kepler
| Suggested the elliptical orbits of planets, and propounded his Laws of Planetary Motion.
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| Isaac Newton
| Published Philosophiae Naturalis Principia Mathematica ( 1687), containing the " Newton's laws of motion", which are fundamental to mechanical physics, and which explained Kepler's laws of planetary motion. Predicted the orbits of the solar planets.
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| Henrietta Swan Leavitt
| Catalogued Cepheid variable stars in the Magellanic Clouds, in 1912 discovered the relationship between luminosty and periodicity in Cepheids -- leading to Hertzprung's later work.
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| Ejnar Hertzsprung
| determined the distance to several Cepheids, when Cepheids were detected in other galaxies such as the Andromeda galaxy, the distance to those galaxies could then be determined.
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| Edwin Hubble
| Discovered the expansion of the universe. ( Hubble's Law) The Hubble Orbiting Space Telescope was named in his honor.
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