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.
After spending the summer reading several basic books on the history of astronomy and stellar measurement, he joined the American Astronomical Society. He finished a jumbled doctoral thesis before going overseas to serve in the army during World War I.
Following his service, Hubble accepted an opportunity for further study at Cambridge. There the aspiring astronomer joined one of the founders of modern astrophysics, George Hale , and his team at the just completed inch reflector telescope on Mt. The iconoclastic pair became close collaborators for the next 34 years. Together they would parlay his image, charisma, and legitimate scientific celebrity into an active Hollywood and international social calendar.
The paper demonstrated a remarkable correspondence between galaxy distance and speed: the farther the faster. The relationship meant that one could create a look-back time to imagine when all of the galaxies exploded outward from a single point of origin, a beginning to the universe. But for a man who seemed in all other ways to enjoy being the center of attention, Hubble remained uncharacteristically reserved. While he acknowledged the concept of the expanding universe, he never held up his work as proof, as others did.
And although from this time forward he would be associated with discovering the origin of the universe, he never made such a claim himself. The relationship between motion and distance soon became known as the Hubble Constant. With it came the birth of modern cosmology—the science of both the history and the fate of the universe. Hubble returned to the University of Chicago to study astronomy at the Yerkes Observatory in , earning his PhD in , and was then offered a staff position by George Ellery Hale, the founder and director of Carnegie Institution's Mount Wilson Observatory, near Pasadena, California.
However, World War I intervened, and Hubble enlisted in the infantry, quickly advancing to the rank of major. On his return to the United States in the summer of l9l9, he went immediately to take up his position at Mount Wilson, where he was to remain until his death, and which was to be the scene of all his major discoveries. His meticulously documented observations, announced at the beginning of , proved conclusively that these nebulae were nearly a million light years away, much too distant to be part of the Milky Way, and were in fact entire galaxies outside our own.
At that time, this was a revolutionary idea, the prevailing view being that the universe consisted entirely of the Milky Way, and it was opposed vehemently by many in the astronomy establishment, particularly by Harvard-based Harlow Shapley, who had made his reputation by measuring the size of the Milky Way. Hubble went on to devise the most commonly used system for classifying galaxies , grouping them according to their appearance in photographic images, in what became known as the Hubble sequence.
But an even more dramatic and important discovery was still to come. Einstein traveled to Mount Wilson to see the telescope and to thank Hubble personally for delivering him from folly. Hubble had married Grace Burke in Pasadena in , and for a time, during the s and s, the Hubbles basked in the celebrity of these important astronomical discoveries.
Hubble had affected British mannerisms and clothing since his time as a young man in Cambridge, and had a tendency towards vanity, pretentiousness and racism, but he was handsome, fit and an imposing presence at well over six feet tall, as well as an engaging conversationalist. Army as head of ballistics at the Aberdeen Proving Ground, for which he received the Legion of Merit decoration. But other famous astronomers disagreed.
Harvard College Observatory manager, Harlow Shapley, one of the first to measure the dimensions of our galaxy, was one of those astronomers.
Van Maanen tried to measure the internal velocity of the spirals; He found that the stars within them moved relative for each other, which meant that they could not be as far away as Hubble believed. Because, even in , light-years, the shift in individual stars would be too small to measure.
Therefore, the spirals must be in our galaxy, Van Maanen said. The disagreement among colleagues at the observatory was also deepened with their dislike to each other. Hubble decided to try a completely different method. He would reference the stars known as Cepheid Variable stars. Many stars, including the sun, shine more or less the same over the centuries, but some are different; some shine and fade at regular, some unpredictable intervals.
The Cepheid Variables, named after Delta Cepheid, the best-known member of the class, have absolute regular periods, ranging from several days to weeks, so that they can always be known how to act; Delta Cepheid, which can be easily seen with the naked eye in the northern hemisphere, has a 5. The relation between the true luminosity and the periods of Cepheids was also known: the luminosity of the star was increasing as the period was extended. Another Northern hemisphere Cepheid, Eta Aquilae has a 7.
If we measure the period of a Cepheid, we can find its luminosity and thus its distance, moreover, all Cepheids are very bright and they can be easily seen from many light-years beyond the galaxy.
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