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| ?4000BC | Oldest recorded astronomical observations (Egypt and Central America) |
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| VI cen BC | Pythagoras and Thales of Miletus speculate that Earth is a sphere. |
| ?270BC | Plato's student Aristarchus of Samos suggests Earth revolves about Sun (model not accepted -- observations showed no moving Earth). |
| ?235BC | Eratosthenes measures circumference of Earth. |
| ?130BC | Hipparchus discovers precession of equinoxes - makes 1st star catlogue and invents star magnitude scale. |
| 45BC | Introduction of Julian calendar in Roman Empire [Sosigenes (Gr)] |
| 140AD | Ptolemy suggests epicycles in geocentric theory in work Mathematike Syntaxis - Arabic translation = Almagest. (Work covers 13 volumes) |
| July 4,1054 | Chinese and Native American astronomers observe supernova in Taurus which is visible in daylight(now Crab Nebula - M1). |
| 1450 | Gutenberg makes first printing press in Europe. |
| 1543 | Copernicus (1473-1543) publishes De Revolutionibus Orbium Coelestium touting heliocentric theory of Universe and dies at age 70. (Had idea since 1514) |
| Nov.,1572 | Tycho Brahe (1546-1601)discovers a supernova in Cassiopeia. |
| 1576 | Tycho Brahe founds observatory Uraniborg on Hven island between Denmark and Sweden -- from King Fredrick II. |
| Oct.15,1582 | Pope Gregory XIII introduces Gregorian calendar. |
| Apr.22,1597 | Brahe forced to leave Hven -- eventually ends up in Prague. |
| 1600 | Brahe employs Johannes Kepler (1571-1630). Brahe dies 10/24/1601. |
| Feb.17,1600 | Giordano Bruno burned at stake (in part for a heliocentric view). |
| 1603 | Johann Bayer star catalogue, Uranometria. (Greek letters for stars) |
| 1604 | Kepler discovers supernova in Ophiuchus. |
| 1608 | Dutch spectacles maker, Hans Lippershey, invents first telescope. |
| 1609 | Galileo Galilei (1564-1642) first uses the telescope for astronomy. |
| 1609 | First 2 of Kepler's 3 Laws of Planetary motion formulated. |
| 1610 | Galileo discovers 4 moons of Jupiter. |
| 1611 | Kepler invents modern refracting telescope. |
| Jan.,1613 | Galileo inadvertantly observes Neptune (officially discovered 1846). |
| 1619 | Kepler's 3rd Law of Planetary motion formulated. |
| 1632 | Galileo publishes Dialogue on the Two Chief World Systems. |
| 1633 | Galileo recants theories before Inquisition. |
| 1656 | Christiaan Huygens discovers the rings of Saturn. |
| 1665 | Giovanni Cassini first observes Red Spot on Jupiter. |
| 1668 | Newton builds the first reflecting telescope (Newtonian reflector). |
| 1676 | Romer measures the velocity of light. |
| 1687 | Sir Isaac Newton (1642-1727) publishes Philosophiae Naturalis Principia Mathematica containing 3 laws of motion and theory of universal gravitation. |
| 1705 | Edmund Halley links 3 previous comet observations- predicts return in 1758. |
| 1781 | Charles Messier publishes his catalogue of comet-like objects. |
| Mar.13,1781 | Sir William Herschel discovers Uranus. |
| Jan.1,1801 | Theatine Sicilian monk Giuseppe Piazzi discovers first and largest asteriod Ceres. |
| 1802 | Wollaston observes dark lines in solar spectrum. |
| 1802 | Sir William Herschel discovers binary stars. |
| 1814 | Fraunhofer provides a detailed description of solar spectrum. |
| 1823 | Heinrich Olbers's paradox-- "Why is the sky dark?" |
| 1838 | First measurement of distance to stars by parallax. |
| 1839-40 | John William Draper takes first photograph of the Moon. |
| 1842 | Christian Doppler theory of Doppler Effect for sound and light. |
| Sep.23,1846 | Johann Galle discovers the planet Neptune (math calculations by Adams and Leverrier working independently). |
| 1848 | William Thomson (Lord Kelvin) develops absolute temperature scale. |
| 1851 | Foucault demonstrates rotation of Earth by long pendulum from dome of the Pantheon in Paris. |
| 1859 | Kirchoff interprets dark lines in star spectra. |
| 1868 | Element helium discovered on Sun's spectrum - before known on Earth |
| 1887 | Michelson and Morley in Cleveland fail to detect ether drift. |
| 1893 | Maunder discovered Sunspot miminum between 1645AD and 1715AD called Maunder Minimum. |
| 1894 | Percival Lowell founds Flagstaff Observatory in Arizona. |
| 1894 | Heinrich Hertz discovers radio waves behave like light waves. |
| 1897 | Yerkes Observatory completed (Houses world’s largest refracting telescope)(40-inch). |
| 1905 | Mount Wilson Observatory founded in Caifornia. |
| 1905 | Einstein proposes Special Theory of Relativity. |
| June 30, 1908 | Asteroid, or comet, or meteorite broke up and exploded over Tunguska, Siberia. |
| 1908-12 | Leavitt discovers relationship between period and absolute Magnitude for Cepheids. |
| 1911-14 | Hertzsprung and Henry Norris Russell (1877-1957) independently discover the relationship between star spectral type and star absolute magnitude (H-R diagram). |
| 1914 | Goddard begins rocket experiments. |
| 1914 | Ejnar Hertzsprung (1893-1967) measures distance to Large Magellanic Cloud using Cepheid variables. |
| 1915 | Einstein proposes his General Theory of Relativity (gravity explained as curvature of geometry of Space-Time). |
| 1917 | 100-inch Hooker reflector built at Mount Wilson in California. |
| 1918 | Shapley provides the first model of the Galaxy structure. |
| 1918-24 | Annie Jump Cannon publishes the fundamental catalogue of star spectra. She reorganized star spectral order in 1901AD. |
| 1924 | Hubble proves that the galaxies lie beyond the Milky Way. |
| 1927 | Oort proves that the center of the galaxy lies in direction of Sagittarius and rotates. |
| 1927 | Father Georges Lemaitre provides a model for an expanding universe. |
| 1929 | Edwin Powell Hubble discovers linear relationship between the galaxy distance and its radial velocity. Galaxies recede from each other. |
| Feb.18,1930 | Clyde Tombaugh (1906-1997)discovers Pluto based on Lowell's predictions. |
| 1931 | Jansky discovers cosmic radio waves. |
| 1931 | Einstein discards cosmological constant -- non static universe. |
| 1932 | Theory of neutron stars (Lev Davidovich Landau) |
| 1933 | Dark matter discovered in galactic clusters. |
| 1934 | Baade and Zwicky propose supervova theory of dying stars. |
| 1935 | Chandrasekhar calculates mass limit of white dwarf star. |
| 1937 | Grote Reber constructs the first radio telescope. |
| 1937-40 | Gamow proposes the first theory of stellar evolution. |
| 1938 | Oppenheimer and Serber predict upper mass limit for neutron stars. |
| 1938 | Theory of CNO nuclear fusion cycle for large stars. |
| 1939 | Theory of black hole forming from collapsing neutron star. |
| 1944 | Walter Baade divides stars into Population I and Population II categories. |
| 1946 | George Gammow proposes cold big bang model. |
| 1948 | Steady state theory of universe proposed. |
| 1949 | Hale 200-inch reflector is completed at Mount Palomar, California. |
| 1949 | Fred Hoyle coins the usage of term "big bang". |
| 1950 | Jan Oort proposes theory of comet origins. |
| 1951 | Gerard Kuiper proposes existence of Kuiper Belt in outer Solar System. |
| 1951-54 | Determination is made of spiral structure of our galaxy. |
| 1955 | Jodrell Bank 250-foot radio telescope is completed. |
| Oct.4,1957 | Sputnik, first artifical satellite launched by Russians. |
| Sept.14,1959 | First spacecraft (Soviet's Lunik II)to impact the Moon. |
| April 12,1961 | First man (Russian Yuri Gargarin) in Earth orbit in Vostok 1. |
| Feb. 20,1962 | First American orbital flight by John Glenn. |
| 1962 | Discovery of first galactic source of X-ray radiation. |
| 1962 | Mariner 2 flies by Venus. |
| 1962 | Penzias and Wilson discover cosmic background radiation - giving evidence of the Big Bang Theory. |
| 1963 | Discovery of first quasar (3C 273). |
| 1965 | Mariner 5 flies by Mars. |
| Feb.3,1966 | First spacecraft soft landing on the Moon (Soviet's Lunik 9). |
| March 1,1966 | Soviet spacecraft (Venera 3) crashes into Venus. First man-made craft to land on another planet. |
| 1967 | John Wheeler coins term "black hole" |
| 1967 | Jocelyn Bell discovers 1st pulsar (LGM-1). |
| July 20,1969 | First 2 men on the Moon (United States' Armstrong and Aldrin of Apollo 11). |
| Dec.15,1970 | First man-made craft to soft land on Venus (Soviet's Venera 7). |
| 1971 | Soviets finish building 236-inch reflector. (6-meter telescope completed in Zielenczukskaja in 1975). |
| 1971 | Mariner 9 orbits Mars. |
| 1972 | Pioneer 10 launched. First probe to Jupiter (arrives 1973). |
| 1972 | Cygnus X-1 identified as black hole. |
| 1972 | Apollo 17 – last humans to visit Moon. |
| 1973 | Discovery of dark matter in galaxies. |
| 1974 | Mariner 10 transmits close up images of Mercury's surface. |
| 1974 | Stephen Hawking predicts black holes can radiate. |
| 1976 | Soft landing of Viking I space probe on Mars. |
| 1977 | Discovery of rings around Uranus. |
| 1978 | Discovery of Pluto's first satellite Charon by James Christy. |
| 1979 | Voyager I discovers rings of Jupiter. |
| 1979 | Pioneer II flies by Jupiter. |
| 1980 | Proposal for inflationary early universe by Alan Guth. |
| 1981 | First space shuttle. |
| Jan.28,1986 | Space shuttle Challenger explodes; 7-killed. |
| March,1986 | Three space probes pass near Halley's Comet. |
| 1986 | Voyager 2 flies by Uranus. |
| Feb.23,1987 | Supernova 1987a in the Large Magellanic Cloud (LMC) visible to naked eye - caused by explosion of blue supergiant Sanduleak 69 deg.202. |
| 1989 | The World Wide Web formed. |
| 1989 | European Space Agency launches Hipparcos satellite to measure stellar parallax more precisely. |
| 1989 | Voyager 2 flies by Neptune. |
| Apr.24,1990 | Twelve ton, 94-inch Hubble Space Telescope goes in orbit. |
| 1991 | Galileo spacecraft first flyby of an asteroid - 951 Gaspera. |
| Apr.24,1992 | Data from COBE satellite proves existence of temperature fluctuations in background radiation further supporting Big Bang. |
| Oct.31,1992 | Vatican (Pope John Paul II) admits Catholic Church error in condemning Galileo's beliefs. |
| Dec.,1993 | Astronauts correct the defects in Hubble Space Telescope. |
| Jul.16,1994 | Comet Shoemaker-Levy 9 crashes into Jupiter (7/16 to 7/22). |
| 1994 | Galileo spacecraft first satellite of an asteroid (243 Ida). |
| 1995 | First extra-solar planet discovered orbiting an ordinary star. |
| Dec.,1995 | Galileo spacecraft parachutes into Jupiter. |
| 1998 | Supernovae observations suggest that expansion of universe is accelerating. |
| 2000 | Shoemaker spacecraft orbits asteroid Eros. |