Abstract

Between 1916 and 1927, Mt. Wilson astronomer Adriaan van Maanen published twelve papers on astrometric measurements of internal motions in what were known then as spiral nebulae. Of special note were the Messier objects M33, M51, M81, and M101. His measured internal motions were of such a magnitude (averaging about 20 milli-arcsecs per year in the peripheries of the objects) that one could imply that the nebulae were close enough to us to be physically associated with the Milky Way. In the 1920 Shapley-Curtis ?Scale of the Universe? debate, Shapley relied heavily on van Maanen's nebular internal motions in his argument for a small universe (Milky Way plus local denizens.) However, by 1937 the quest to prove the existence of an expanding universe, which was driven by a desire to satisfy Einstein-Lema?tre cosmology, aided by Hubble's interpretation of cosmological redshift as a velocity effect, buried van Maanen's findings. Astronomers, in general, decided that van Maanen had made some kind of never explained procedural error and there was no reason to do any further internal motion measurements on spiral nebulae. Spiral nebulae became renamed ?galaxies? and in general were relegated to great distances from the Milky Way as other island universes. Van Maanen never recanted his findings. It seems that ongoing angular velocity measurements of galaxies can validate van Maanen's measurements or finally put them to rest. If they are validated, then Big Bang theory is in serious trouble from a new quarter.