Published in 1926, 'Extra-Galactic Nebulae' by Edwin Hubble is a scientific work that classifies and investigates 400 extra-galactic nebulae, which are celestial formations outside the Milky Way. Hubble provides a statistical analysis of these nebulae, revealing that about 97% exhibit regular forms, while a minority are irregular. The book discusses the relationships between luminosity, apparent size, and distance, contributing significantly to the understanding of the cosmos and the evolutionary phases of astronomical bodies.
