1848 — Lord Rosse studies M1 and names it the Crab Nebula. The telescope is much larger than the small refactors typical of this period and it also reveals the spiral nature of M51.
1965 — James Gunn and Bruce Peterson use observations of the relatively low absorption of the blue component of the Lyman-alpha line from 3C9 to strongly constrain the density and ionization state of the intergalactic medium[4]
1990 — Foreground "contamination" data from the COBE spacecraft provides the first all-sky map of the ISM in microwave bands.
Referencesedit
^Kanipe, Jeff (2011-01-27). The Cosmic Connection: How Astronomical Events Impact Life on Earth. Prometheus Books. ISBN 9781591028826.
^ ab"V. M. Slipher Papers, 1899-1965". www.azarchivesonline.org. Retrieved 2019-11-29.
^Ewen, H. I.; Purcell, E. M. (September 1951), "Observation of a Line in the Galactic Radio Spectrum: Radiation from Galactic Hydrogen at 1,420 Mc./sec.", Nature, 168 (4270): 356, Bibcode:1951Natur.168..356E, doi:10.1038/168356a0, S2CID 27595927
^Gunn, James E.; Peterson, Bruce A. (November 1965), "On the Density of Neutral Hydrogen in Intergalactic Space", Astrophysical Journal, 142: 1633–1641, Bibcode:1965ApJ...142.1633G, doi:10.1086/148444
^Wilson, R. W.; Jefferts, K. B.; Penzias, A. A. (July 1970), "Carbon Monoxide in the Orion Nebula", Astrophysical Journal, 161: L43, Bibcode:1970ApJ...161L..43W, doi:10.1086/180567