- Timeline of knowledge about galaxies, clusters of galaxies, and large-scale structure
Timeline of galaxies, clusters of galaxies, andlarge-scale structure of the cosmos Pre-20th Century
* 400s BC -
Democritus proposes that the bright band in the night sky known as theMilky Way might consist ofstar s,
* 300s BC -Aristotle believes the Milky Way to be caused by "the ignition of the fiery exhalation of some stars which were large, numerous and close together" and that the "ignition takes place in the upper part of theatmosphere , in the region of the world which is continuous with the heavenly motions",cite web|author=Josep Puig Montada|title=Ibn Bajja|publisher=Stanford Encyclopedia of Philosophy |url=http://plato.stanford.edu/entries/ibn-bajja|date=September 28, 2007|accessdate=2008-07-11]
* 964 AD -Abd al-Rahman al-Sufi (Azophi), a Persian astronomer, makes the first recorded observations of theAndromeda Galaxy cite book |last= Kepple |first= George Robert |coauthors= Glen W. Sanner |title= The Night Sky Observer's Guide, Volume 1 |publisher= Willmann-Bell, Inc. |year= 1998 |id= ISBN 0-943396-58-1 |pages=18] and theLarge Magellanic Cloud cite web | title=Observatoire de Paris (Abd-al-Rahman Al Sufi) | url=http://messier.obspm.fr/xtra/Bios/alsufi.html | accessdate=2007-04-19 ] cite web | title=Observatoire de Paris (LMC) | url=http://messier.obspm.fr/xtra/ngc/lmc.html | accessdate=2007-04-19 ] in his "Book of Fixed Stars ", and which are the first galaxies other than the Milky Way to be observed from Earth,
* 1000s -Abū Rayhān al-Bīrūnī , another Persian astronomer, describes theMilky Way galaxy as a collection of numerous nebulous stars, [MacTutor Biography|id=Al-Biruni|title=Abu Rayhan Muhammad ibn Ahmad al-Biruni]
* 1000s -Ibn al-Haytham (Alhazen), an Arabian astronomer, refutes Aristotle's theory on the Milky Way by making the first attempt at observing and measuring the Milky Way'sparallax , [citation|title=Great Muslim Mathematicians|first=Mohaini|last=Mohamed|year=2000|publisher=Penerbit UTM|isbn=9835201579|pages=49-50] and he thus "determined that because the Milky Way had no parallax, it was very remote from theearth and did not belong to the atmosphere", [cite web|title=Popularisation of Optical Phenomena: Establishing the First Ibn Al-Haytham Workshop on Photography|author=Hamid-Eddine Bouali, Mourad Zghal, Zohra Ben Lakhdar|publisher=The Education and Training in Optics and Photonics Conference|year=2005|url=http://spie.org/etop/ETOP2005_080.pdf|accessdate=2008-07-08]
* 1100s -Ibn Bajjah (Avempace) of Islamic Spain proposes the Milky Way to be made up of many stars but that it appears to be a continuous image due to the effect ofrefraction in theEarth's atmosphere ,
* 1300s -Ibn Qayyim Al-Jawziyya ofSyria proposes the Milky Way galaxy to be "a myriad of tiny stars packed together in the sphere of the fixed stars" and that these stars are larger thanplanet s,citation|title=Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation|first=John W.|last=Livingston|journal=Journal of the American Oriental Society|volume=91|issue=1|date=1971|pages=96-103 [99] ]
*1521 -Ferdinand Magellan observes theMagellanic Clouds during his circumnavigating expedition,
*1610 -Galileo Galilei uses atelescope to determine that the bright band on thesky , the "Milky Way ", is composed of many faintstar s,
*1750 - Thomas Wright discusses galaxies and the shape of the Milky Way,
*1755 - Drawing on Wright's work,Immanuel Kant conjectures that the galaxy is a rotating disk of stars held together bygravity , and that thenebula e are separate such galaxies,
*1845 - Lord Rosse discovers a nebula with a distinct spiral shapeEarly 20th Century
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1918 -Harlow Shapley demonstrates thatglobular cluster s are arranged in a spheroid or halo whose center is not theEarth , decides, correctly, that its center is the center of the galaxy,
*1920 - Harlow Shapley andHeber 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 usesopen cluster observations to quantify the absorption oflight byinterstellar dust in thegalactic plane ; this absorption had plagued earlier models of the Milky Way,
*1932 -Karl Guthe Jansky discoversradio noise from the center of the Milky Way,
*1933 -Fritz Zwicky applies thevirial theorem to theComa Cluster and obtains evidence for unseenmass ,
*1936 - Edwin Hubble introduces the spiral, barred spiral, elliptical, and irregular galaxy classifications,
*1939 -Grote Reber discovers the radio sourceCygnus A ,
*1943 -Carl Keenan Seyfert identifies six spiral galaxies with unusually broademission line s, named Seyfert galaxies,
*1949 - J.G. Bolton, G.J. Stanley, and O.B. Slee identify NGC 4486 (M87) andNGC 5128 as extragalactic radio sources,Mid-20th Century
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1953 -Gerard de Vaucouleurs discovers that the galaxies within approximately 200 millionlight year s of theVirgo cluster are confined to a giantsupercluster disk,
*1954 -Walter Baade andRudolph Minkowski identify the extragalactic optical counterpart of the radio source Cygnus A,
*1959 - Hundreds of radio sources are detected by theCambridge 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" source3C 48 to within 5",
*1960 -Allan Sandage optically studies3C 48 and observes an unusual blue quasistellar object,
*1962 -Cyril Hazard , M.B. Mackey, and A.J. Shimmins uselunar occultation s to determine a precise position for thequasar 3C 273 and deduce that it is a double source,
*1962 -Olin Eggen ,Donald Lynden-Bell , andAllan Sandage theorizegalaxy 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 quasar3C 273
*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,
*1973 - Donald Gudehus finds that the diameters of the brightest cluster galaxies have increased due to merging,
*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 theluminosity of an elliptical galaxy and thevelocity dispersion in its center. In 1991 the relation is revised by Donald Gudehus,
*1977 -R. Brent Tully andRichard Fisher publish the Tully-Fisher relation between the luminosity of an isolated spiral galaxy and the velocity of the flat part of itsrotation curve ,
*1978 - Steve Gregory andLaird Thompson describe the Coma supercluster,
*1978 -Donald Gudehus finds evidence that clusters of galaxies are moving at several hundred kilometers per second relative to the cosmic microwave background radiation,
*1978 -Vera Rubin ,Kent Ford , N. Thonnard, andAlbert 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 andRobert Zinn theorize thatgalaxy formation occurs through the merger of smaller groups.Late 20th Century
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1981 -Robert Kirshner ,August Oemler ,Paul Schechter , andStephen Shectman find evidence for a giant void inBoötes with a diameter of approximately 100 million light years,
*1985 -Robert Antonucci and J. Miller discover that the Seyfert II galaxyNGC 1068 has broad lines which can only be seen in polarized reflected light,
*1986 -Amos Yahil ,David Walker , andMichael Rowan-Robinson find that the direction of theIRAS galaxy densitydipole agrees with the direction of thecosmic microwave background temperature dipole,
*1987 -David Burstein ,Roger Davies ,Alan Dressler , Sandra Faber,Donald Lynden-Bell , R.J. Terlevich, andGary 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 andCentaurus ,
*1989 -Margaret Geller andJohn 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 andTom Broadhurst discover that the IRAS galaxyIRAS F10214+4724 is the brightest known object in theUniverse ,
*1991 -Donald Gudehus discovers a serious systematic bias in certain cluster galaxy data (surface brightness vs. radius parameter, and the D_n method) which affect galaxy distances and evolutionary history; he devises a new distance indicator, the reduced galaxian radius parameter, r_g, which is free of biases,
*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 thecosmic microwave background
*1995 -Hubble Deep Field survey of galaxies in field 144 arc seconds across.
*1998 - The2dF 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 ofaccelerating universe
*2000 - Data from several cosmic microwave background experiments give strong evidence that the Universe is "flat" (space is not curved, although space-time is), with important implications for the formation of large-scale structureEarly 21st Century
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2001 - First data release from the on-goingSloan Digital Sky Survey
*2004 - TheEuropean Southern Observatory discoversAbell 1835 IR1916 , the most distant galaxy yet seen from Earth.
*2004 - TheArcminute Microkelvin Imager begins to map the distribution of distant clusters of galaxiesee also
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Large-scale structure of the cosmos References
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