Astronomy of the 20th Century

Astronomy of the 20th Century

The 20th century brought many new developments to the study of space. Huge telescopes, such as the 10-m (400-in) Keck telescopes, came into use. Astronomers began to use the Hubble Space Telescope and other space-based observatories. They also began to measure and record radiation that is not visible to the human eye.

Period

Year

Event

1900-1919	1905	Einstein states the special theory of relativity.
	1908	Hertzsprung classifies stars by their brightness: dwarfs and giants.
	1912	The period-luminosity correlation of Cepheids is calculated by H. Leavitt.
	1916	Einstein publishes the general theory of relativity.
	1917	The mirror of the Mount Wilson telescope (2.5 m) is put into use.
1920-1939	1923	Hubble discovers that spiral nebulas are galaxies outside the Milky Way.
	1929	Hubble suggests that the universe is expanding.
	1930	Tombaugh discovers Pluto.
	1931	The first radio waves in space are observed by Jansky.
	1937	With a radio telescope, Reber observes radio radiation from the Milky Way.
	1938	Hans Bethe states the theory of nuclear energy, source of star radiation.
1940-1949	1942	Discovery of radio emissions from the Sun by the team of Hey.
	1946	Identification of the most powerful radio source in the sky (Cygnus A) by Hey, Phillips, and Parsons.
	1948	Use of the 5-m telescope on Mount Palomar (California) begins. Cosmological theory of the stationary universe presented by Bond and Gold. Big bang theory and the origin of elements is developed by Alpher and Gamow.
1950-1959	1952	The scale of the distance to the galaxies is doubled by Baade.
	1957	Launch of the first Sputnik: The era of space conquest opens.
	1959	The Soviet probe Luna 3 takes the first pictures of the hidden side of the Moon.
1960-1969	1961	Gagarin takes the first piloted space flight.
	1962	The first planetary mission succeeds: The United States probe Mariner 2 flies past Venus.
	1963	The first quasar is discovered by Schmidt at Mount Palomar.
	1965	Discovery of radio radiation in deep space at 3 K by Penzias and Wilson.
	1967	Bell Burnell discovers pulsars at Cambridge (Great Britain). V. Komarov (USSR) is the first human victim of a space flight.
	1969	The mission Apollo 11 (Armstrong and Aldrin) puts the first human on the Moon.
1970-1974	1971-1972	The U.S. probe Mariner 9 orbits Mars and gathers the first images.
	1973	First flight past Jupiter by Pioneer 10. A telescope 4 m in diameter is put into service at Kitt Peak (Arizona).
	1974	The probe Mariner 10 registers the first surface details of Mercury and of the atmosphere of Venus.
1975-1979	1975	Soviet space probes Verena 9 and 10 take the first photographs of the Sun from Venus. U.S.-Soviet space docking of Apollo-Soyuz.
	1976	U.S. probes Viking 1 and 2 land on Mars (first measurements of the atmosphere and surface).
	1977	Kowal discovers the asteroid Chiron within the solar system. Discovery of Uranus's rings.
	1978	Christy discovers Charon, Pluto's satellite.
	1979	Launch of two U.S. probes, Voyager 1 and 2, which fly past Jupiter. Pioneer 11 achieves the first flyby of Saturn.
1980-1984	1980	Long baseline interferometer is put into service in New Mexico.
	1980-1981	First detailed study of Saturn and its rings by U.S. probes Voyager 1 and 2.
	1981	First flight of the U.S. space shuttle. Second flyby of Saturn by Voyager 2.
	1983	First infrared scanning of space, by the Infrared Astronomy Satellite (IRAS), starts.
	1984	First in-space repair of an artificial satellite.
1985-1989	1985-1986	Observation of Halley's Comet by different Soviet, European, and Japanese probes.
	1986	Flyby of Uranus by Voyager 2. U.S. space shuttle Challenger explodes in flight.
	1987	Supernova 1987A appears in the Large Magellanic Cloud.
	1988	Record human stay in space: V. Titov and M. Manarov return to Earth after a one-year-long space flight.
	1989	Voyager 2 flies by Neptune. Discovery of dense 'walls' and empty spaces in the spatial distribution of galaxies, by Geller and Uchra. Two U.S. probes are launched: Magellan towards Venus, and Galileo towards Jupiter.
1990-1999	1990	Launch of the Hubble Space Telescope; defectiveness of mirror is discovered. First radar cartography of Venus made by Magellan.
	1992	Two signals almost as old as the universe itself are registered by the satellite COBE. Service of the telescope Keck, 10 m in diameter, begins.
	1993	In-space repair of the Hubble Space Telescope.
	1994	Fragmented comet Shoemaker-Levy collides with Jupiter.
	1995	European Solar and Heliophysical Observatory (SOHO) launched to study the Sun.
	1996	Mars Pathfinder and Sojourner rover explore the surface of Mars.
	1998	Voyager 1 becomes most distant human-made object from Earth. Construction of the International Space Station begins.
	1999	Mars Global Surveyor begins systematic mapping of Mars.