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The main stones of Stonehenge are put into place.
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First solar-lunar calendars
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Aristarchus suggests the Earth revolves around the Sun. He provides first estimation of Earth-Sun distance.
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Eratosthenes measures the circumference of the earth with surprising accuracy
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Hipparchus develops the first accurate star map and star catalog with over 850 of the brightest stars.
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Introduction of the Julian calendar, a purely solar calendar, to the Roman Empire.
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Ptolemy suggests geocentric theory of the universe in famous work Mathematike Syntaxis
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Al Mamon founds the Baghdad school of astronomy.
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Chinese astronomers observe supernova in Taurus.
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Construction of an observatory in Cairo was begun in 1120 A.D. This is possibly the first observatory built in Medieval Islam. Unfortunately, the patron of the observatory was found guilty of several crimes including communication with Saturn, and was sentenced to death. The observatory was then destroyed in 1125 A.D. and the personnel were forced to flee for their lives.
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An observatory was built for the famous Persian astronomer, Nasir al-Din al-Tusi. The patron of the observatory was Mongol ruler, Hulagu, who was addicted to astrology. The observatory, built upon a flattened hill, was named Maragha observatory. The observatory included an extensive library and many instruments set up in the open air.
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Ulugh Beg (1394-1449), noted astronomer, had an observatory built at Samarkand in central Asia. The observatory was a 3-story building, but also contained instruments that were outdoors. Ulugh Beg's observatory produced astronomical tables that included a catalogue of over 1,000 stars. His observatory had enjoyed three decades of existence. And he is remembered as perhaps the most important observational astronomer of the 15th century.
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Copernicus publishes his heliocentric theory of the Universe.
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Tycho Brahe discovers a supernova in constellation of Cassiopeia
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Pope Gregory XIII introduces the Gregorian calendar.
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Johann Bayer introduces Bayer designation of stars, assigning Greek letters to stars, still in use today.
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Hans Lippershey, a Dutch spectacles maker invents the telescope.
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Galileo uses telescope for astronomical purposes. He discovers 4 Jovian moons, the Moon's craters and the Milky Way galaxy.
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Kepler's First and Second Laws of Planetary Motions are announced.
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The Third Law of Planetary Motion is announced by Kepler in his work Harmonice Mundi (Harmony of the World).
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Christian Huygens discovers Saturn's rings and Titan, the fourth satellite of Saturn
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Huygens notes markings on Mars.
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Martian polar ice caps are noted by Cassini.
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The first reflecting telescope was built by Newton.
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Geminiano Montanari discovers the star Algol is not steady in brightness, thus recognizing the first variable star.
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While in Paris, Danish astronomer Ole Romer measures the speed of light.
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Cassini discovers that Saturn's rings are split into two parts, so that today the gap is called the "Cassini Division".
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Newton publishes his theory of universal gravitation in the work Philosophiae Naturalis Principia Mathematica. This is seen to be the start of Modern Astronomy.
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Halley correctly predicts the return of a comet (Halley's comet) in 1758.
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Johann Palitzsch observes Halley's comet as predicted by Halley in 1705.
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The discovery of Uranus by Herschel
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Messier discovers galaxies, nebula and star clusters while looking for comets. He compiles a catalogue of these objects (Messier objects).
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Piazzi discovers first asteroid, Ceres.
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Samuel Heinrich Schwabe describes the sunspot cycle.
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Johann Galle observes and discovers Neptune. His observations were prompted by mathematical calculations by French astronomer Joseph Leverrier and English astronomer John Couch Adams.
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Rocket pioneer Konstantin Tsiolkovskii was born. Tsiolkovskii's work in early rocketry earned him the title of "Father of Astronautics". Many of his proposals concerning rocketry were later put into use including: use of liquid hydrogen and liquid oxygen as rocket fuel and multi-stage rocket design for achieving Earth orbit or interplanetary flight.
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The beginning of spectral analysis of stars by Sir William Huggins
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Jansen and Lockyer observe solar prominences.
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Henry Draper takes a photograph of the stellar spectrum of Vega. This is the first of its kind.
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Asaph Hall discovers Phobos and Deimos, the moons of Mars.
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Schiaparelli observes the canals on Mars.
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The Great Red Spot on Jupiter becomes prominent.
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Mount Wilson Observatory was established for study of the Sun.
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Albert Einstein introduces special Theory of Relativity in paper Electrodynamics of Moving Bodies.
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Hertzsprung describes giant and dwarf stars.
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Henrietta Swan Leavitt discovers Cepheid variables.
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Robert Goddard begins practical rocketry.
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Albert Einstein introduces his general Theory of Relativity.
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Hubble shows that galaxies exist outside the Milky Way galaxy.
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Oort shows the center of the Milky Way galaxy is in Sagittarius