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]
^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,
S2CID27595927
^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