ABSTRACT
Modern cosmology has a precise birthdate, Hubble’s discovery of Cepheids and ordinary stars in Nebulae. The nature of nebulae had been disputed for centuries. As early as 1755, in his General History of Nature and Theory of the Sky, Immanuel Kant suggested that nebulae could be galaxies. The main objection to this hypothesis has been supernovae. Today we know that, close to its peak, a supernova can exceed the luminosity of its host galaxy. But, while this remained unknown, single stars as luminous as whole nebulae were a severe objection to the claim that nebulae were made of as many as hundreds of billions stars. For instance, in 1893, the British astronomer Mary Clark reported the observation of two stellar bursts in a single nebula, one 25 years after the other. She wrote that: The light of the nebula has been practically cancelled by the bursts, which. . . should have been of an order of magnitude so large, that even our imagination refuses in conceiving it. Clark was not alone in having problems conceiving the energetics of supernovae.
