The redshift of extragalactic nebulae

The important, lasting result of Fritz Zwicky’s early paper on extragalactic astrophysics, which is not mentioned in the abstract, is his conclusion, derived in Sect. 5, that the universe contains much more dark than luminous matter. This result is embedded in a review of what was known about “nebulae” and their redshift in 1933. The first methods to determine distances of galaxies and their distribution on the sky and in space are summarized, and explanations for their redshift are considered. In this note I shall make remarks on the changes of quantitative data and comment on the history of the theory of extragalactic redshifts and on Zwicky’s attempt to relate the just discovered cosmic radiation to those redshifts. The distance and diameter of the Andromeda galaxy, given by Zwicky in Sect. 2A as 900 resp. 42kly (kilo light years), are based on the Cepheidmethod used byHubble. The present values are about 2,500 resp. 100kly. The large “increase” of these values is due to Baade’s discovery [1] of two types of Cepheids with different period-luminosity relations, belonging to distinct stellar populations, and Sandage’s identification of Hubble’s “brightest stars” asHII regions,which aremuchmore luminous than stars [2].