1.2. Hubble's legacy
Why then was the telescope eventually named for Edwin Hubble? That too is appropriate, but much farther back in history. Simply, Hubble had manufactured the foundations upon which a large part of the present work of the telescope on cosmology is centered.
In only 12 years from 1924 to 1936, Hubble brought to an almost modern maturity the four foundations of observational cosmology, even as its principles are practiced today.
(1) He proved that nebulae are galaxies by identifying the content of NGC 6822, M33, and M31 (Hubble 1925, 1926a, 1929a) to be stars similar to those in the Milky Way.
(2) From an early beginning in 1922, he perfected the galaxy classification system (Hubble 1926b, 1936c) that undoubtedly contains clues to galaxy formation and evolution. Hubble's proposal, now universally adopted, was more systematic than that of Lundmark (1926, 1927), but there are obvious similarities, especially as to names. Lundmark introduced three groups as "amorphous ellipticals," "true spiral," and "magellanic cloud types." A flavor of a rivalry between these two giants is seen in Lundmark's (1927) footnote rebutting Hubble's (1926b) perhaps unjustified attack on Lundmark, also in a footnote.
(3) He organized existing data on redshifts and apparent magnitudes (Hubble 1929b) of nearby galaxies into a believable redshift-distance relation, searched for throughout the 1920s as the "de Sitter effect" by many others (Wertz [the European Hubble without a telescope], Truman, Silberstein, Lundmark) but without success, and seen in the early data as adumbrations by Lemaitre (1927, 1931) and Robertson (1928). Hubble, with Humason, then greatly extended the velocity-distance relation into the "remote" expansion field (Hubble & Humason 1931, 1934: Humason 1936; Hubble 1936a, 1937, 1953).
(4) He made a massive observational program of galaxy counts for the N(m) function, from which he attempted to measure the curvature of space (Hubble 1934, 1936b, c, 1937, 1953).
More detail on the history of these developments is the subject of this review. Most emphasis is placed on galaxy counts (item 4) as buttressed by data on redshifts and magnitudes (item 3) as needed for the interpretation. A few comments on the role of the abnormal galaxy morphology at faint magnitudes in the HDF, (item 2), closes the review.