- 1918 - Harlow Shapley demonstrates that Globular Cluster s are arranged in a spheroid or halo whose center is not the Earth , decides, correctly, that its center is the center of the galaxy,
- 1920 - Harlow Shapley and Heber Curtis debate whether or not the spiral nebulae lie within the Milky Way,
- 1923 - Edwin Hubble resolves the Shapely-Curtis debate by finding Cepheids in Andromeda ,
- 1930 - Robert Trumpler uses Open Cluster observations to quantify the Absorption of Light by Interstellar Dust in the Galactic Plane ; this absorption had plagued earlier models of the Milky Way,
- 1932 - Karl Guthe Jansky discovers Radio Noise from the center of the Milky Way,
- 1933 - Fritz Zwicky applies the Virial Theorem to the Coma Cluster and obtains evidence for unseen Mass ,
- 1936 - Edwin Hubble introduces the spiral, barred spiral, elliptical, and irregular galaxy classifications,
- 1939 - Grote Reber discovers the radio source Cygnus A ,
- 1943 - Carl Keenan Seyfert identifies six spiral galaxies with unusually broad Emission Line s, named Seyfert Galaxies ,
- 1949 - J.G. Bolton, G.J. Stanley, and O.B. Slee identify NGC 4486 ( M87 ) and NGC 5128 as extragalactic radio sources,
- 1953 - Gerard De Vaucouleurs discovers that the galaxies within approximately 200 million Light Year s of the Virgo Cluster are confined to a giant Supercluster disk,
- 1954 - Walter Baade and Rudolph Minkowski identify the extragalactic optical counterpart of the radio source Cygnus A,
- 1959 - Hundreds of radio sources are detected by the Cambridge Interferometer which produces the 3C Catalogue . Many of these are later found to be distant quasars and radio galaxies
- 1960 - Thomas Matthews determines the radio position of the '' 3C '' source 3C48 to within 5",
- 1960 - Allan Sandage optically studies 3C48 and observes an unusual blue quasistellar object,
- 1962 - Cyril Hazard , M.B. Mackey, and A.J. Shimmins use Lunar Occultation s to determine a precise position for the Quasar 3C273 and deduce that it is a double source,
- 1962 - Olin Eggen , Donald Lynden-Bell , and Allan Sandage theorize Galaxy Formation by a single (relatively) rapid monolithic collapse, with the halo forming first, followed by the disk.
- 1963 - Maarten Schmidt identifies the redshifted Balmer lines from the quasar 3C273
- 1973 - Jeremiah Ostriker and James Peebles discover that the amount of visible matter in the disks of typical spiral galaxies is not enough for Newtonian gravitation to keep the disks from flying apart or drastically changing shape,
- 1974 - B.L. Fanaroff and J.M. Riley distinguish between edge-darkened (FR I) and edge-brightened (FR II) radio sources,
- 1976 - Sandra Faber and Robert Jackson discover the Faber-Jackson relation between the Luminosity of an elliptical galaxy and the Velocity dispersion in its center,
- 1977 - R. Brent Tully and Richard Fisher publish the Tully-Fisher relation between the luminosity of an isolated spiral galaxy and the velocity of the flat part of its Rotation Curve ,
- 1978 - Steve Gregory and Laird Thompson describe the Coma supercluster,
- 1978 - Vera Rubin , Kent Ford , N. Thonnard, and Albert Bosma measure the rotation curves of several spiral galaxies and find significant deviations from what is predicted by the Newtonian gravitation of visible stars,
- 1978 - Leonard Searle and Robert Zinn theorize that Galaxy Formation occurs through the merger of smaller groups.
- 1981 - Robert Kirshner , August Oemler , Paul Schechter , and Stephen Shectman find evidence for a giant void in Boötes with a diameter of approximately 100 million light years,
- 1985 - Robert Antonucci and J. Miller discover that the Seyfert II galaxy NGC 1068 has broad lines which can only be seen in Polarized reflected light,
- 1986 - Amos Yahil , David Walker , and Michael Rowan-Robinson find that the direction of the IRAS galaxy density Dipole agrees with the direction of the Cosmic Microwave Background temperature dipole,
- 1987 - David Burstein , Roger Davies , Alan Dressler , Sandra Faber , Donald Lynden-Bell , R.J. Terlevich, and Gary Wegner claim that a large group of galaxies within about 200 million light years of the Milky Way are moving together towards the " Great Attractor " in the direction of Hydra and Centaurus ,
- 1989 - Margaret Geller and John Huchra discover the " Great Wall ", a sheet of galaxies more than 500 million light years long and 200 million wide, but only 15 million light years thick,
- 1990 - Michael Rowan-Robinson and Tom Broadhurst discover that the IRAS galaxy IRAS F10214+4724 is the brightest known object in the Universe ,
- 1992 - First detection of large-scale structure in the Cosmic Microwave Background indicating the seeds of the first clusters of galaxies in the early Universe
- 1995 - First detection of small-scale structure in the Cosmic Microwave Background
- 1995 - Hubble Deep Field survey of galaxies in field 144 arc seconds across.
- 1998 - The 2dF Galaxy Redshift Survey maps the large scale structure in a section of the Universe close to the Milky Way
- 1998 - Hubble Deep Field South
- 1998 - Discovery of Accelerating Universe
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