The Universe was much bigger than had been previously presumed. Hubble wanted to classify the galaxies according to their content, distance, shape, and brightness patterns, and in his observations he made another momentous discovery: By observing redshifts in the light wavelengths emitted by the galaxies, he saw that galaxies were moving away from each other at a rate constant to the distance between them Hubble's Law.
The further away they were, the faster they receded. This led to the calculation of the point where the expansion began, and confirmation of the big bang theory. Hubble calculated it to be about 2 billion years ago, but more recent estimates have revised that to 20 billion years ago.
An active anti-fascist, Hubble wanted to joined the armed forces again during World War II, but was convinced he could contribute more as a scientist on the homefront. He found that it contained stars just like the ones in our galaxy, only dimmer.
One star he saw was a Cepheid variable, a type of star with a known, varying brightness that can be used to measure distances. From this Hubble deduced that the Andromeda Nebula was not a nearby star cluster but rather an entire other galaxy, now called the Andromeda galaxy. In the following years he made similar discoveries with other nebulae. By the end of the s, most astronomers were convinced that our Milky Way galaxy was but one of millions in the universe.
This was a shift in thought as profound as understanding the world was round and that it revolved around the sun. Hubble then went one step further.
By the end of that decade he had discovered enough galaxies to compare to each other. He created a system for classifying galaxies into ellipticals, spirals and barred spirals — a system called the Hubble tuning fork diagram, used today in an evolved form. But the most astonishing discovery Hubble made resulted from his study of the spectra of 46 galaxies, and in particular of the Doppler velocities of those galaxies relative to our own Milky Way galaxy. What Hubble found was that the farther apart galaxies are from each other, the faster they move away from each other.
Based on this observation, Hubble concluded that the universe expands uniformly. In l, he returned to the University of Chicago for postgraduate work leading to a doctoral degree in astronomy.
After combat service in France during World War I, Hubble was mustered out of the army as a major in l9l9 after which he accepted the offer to work at the Mount Wilson Observatory. When Hubble began his career there, it was thought that the known universe was within the Milky Way galaxy, which was the only galaxy in existence. He found that it contained stars just like the ones in the Milky Way galaxy, only dimmer.
Soon Hubble deduced that the Andromeda Nebula was not a nearby star cluster but rather an entire galaxy, which is now called the Andromeda galaxy.
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