11th century — Alhazen (Ibn al-Haytham), an Arabian astronomer, refutes Aristotle's theory on the Milky Way by making the first attempt at observing and measuring the Milky Way's parallax, and he thus "determined that because the Milky Way had no parallax, it was very remote from the Earth and did not belong to the atmosphere",
14th century — Ibn Qayyim Al-Jawziyya of Syria 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 than planets,
1785 — William Herschel carried the first attempt to describe the shape of the Milky Way and the position of the Sun in it by carefully counting the number of stars in different regions of the sky. He produced a diagram of the shape of the galaxy with the solar system close to the center.
1845 — Lord Rosse discovers a nebula with a distinct spiral shape
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, the diameters of the faintest cluster galaxies have decreased due to tidal distention, and that the Virgo cluster has a substantial peculiar velocity,
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, 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,
1991 — Donald Gudehus discovers a serious systematic bias in certain cluster galaxy data (surface brightness vs. radius parameter, and the method) which affect galaxy distances and evolutionary history; he devises a new distance indicator, the reduced galaxian radius parameter, , 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
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 structure
2013 — The galaxy Z8 GND 5296 is confirmed by spectroscopy to be one of the most distant galaxies found up to this time. Formed just 700 million years after the Big Bang, expansion of the universe has carried it to its current location, about 30 billion light years away from Earth.
^Livingston, John W. (1971). "Ibn Qayyim al-Jawziyyah: A Fourteenth Century Defense against Astrological Divination and Alchemical Transmutation". Journal of the American Oriental Society (American Oriental Society) 91 (1): 96–103 . doi:10.2307/600445. JSTOR600445.