What was the title of Edwin Hubble's Ph.D. thesis?

Edwin Hubble’s Ph.D. thesis was titled “Photographic Investigations of Faint Nebulae.”

Hubble completed the dissertation at the University of Chicago’s Yerkes Observatory and received his doctorate in 1917. The work focused on photographing faint, hazy celestial objects then commonly called nebulae, including objects whose true nature was not yet understood.

The title reflects astronomy’s terminology before the modern distinction between nebulae and galaxies became widely accepted. Hubble later helped establish that many spiral nebulae were actually distant galaxies beyond the Milky Way. His studies of variable stars in Andromeda provided crucial evidence for that conclusion.

A common mix-up is confusing the thesis with Hubble’s later discoveries. “The Expansion of the Universe” describes a major cosmological result associated with his observations, but it was not the title of his dissertation. Hubble’s thesis was an observational study of faint nebulae, not a finished statement of cosmic expansion.