In Chapter eight of our series ‘Discovering Mount Wilson,’ we showcase Edwin Hubble’s discovery of the true nature of the extragalactic universe, with the use of the 100-inch telescope.
Edwin Hubble (1889-1953) joined the staff of Mount Wilson in 1919 right around the same time as the 100-inch telescope began regular science observations. At the time, astronomers were used to seeing conspicuous objects known as spiral nebulae. But, whether they were nearby clouds of dust and gas, or very distant stellar systems, was a matter of vigorous debate.
To get a better idea of the structure of these objects, Hubble used the 100-inch to take extremely detailed measurements of several spiral nebulae. During one such observation on October 5-6, 1923, while observing the Andromeda Nebula, he identified what he thought was a nova, but was proven in subsequent photographs as a Cepheid variable star.
Cepheids are variable stars useful for determining distances by measuring their luminosity and their periods of variability. As the search for Cepheids expanded to other spiral nebulae, Hubble calculated distances that proved these nebulae were too distant to be a part of the Milky Way and were, in fact, entire galaxies outside of our own.
Henrietta Swan Leavitt derived the period-luminosity relationship for Cepheid variable stars in 1912. Hubble used it to discover that nebulae he saw could not lie within the Milky Way, and that these objects were actually galaxies beyond the Milky Way, thus proving the Milky Way is not the entire universe.
Although met with great resistance from fellow scientists, Hubble’s findings fundamentally changed our understanding of the true nature of the universe and our place in it.
