American astronomer Edwin Hubble’s revolutionary work on galaxies led to the formulation of the big bang theory.
American astronomer Edwin Hubble's impact on science has been compared to the contributions of pioneering scientists such as English physicist Isaac Newton and Italian astronomer Galileo Galilei. Hubble helped change the perception of the universe in two important ways. In an era when the Milky Way was perceived as the extent of the entire universe, Hubble confirmed the existence of other galaxies through his observations from the Mount Wilson Observatory in Pasadena, California. Along with other astronomers of his time, Hubble showed that the newly discovered universe was expanding. He also developed a mathematical concept to quantify this expansion, now known as Hubble's law.
Excels as student and athlete
Edwin Powell Hubble was born on November 20, 1889, in Marshfield, Missouri, to John P. Hubble, an insurance agent, and Virginia Lee James Hubble, a descendant of the American colonist Miles Standish. The third of seven children, Hubble spent his early childhood in Missouri, entering grade school in 1895. In 1898, when his father was transferred to the Chicago office of his firm, the Hubble family moved first to Evanston and then to Wheaton, Illinois, both Chicago suburbs.
Hubble attended Wheaton High School, excelling in both sports and academics. He graduated in 1906 at the age of sixteen, two years earlier than most students. For his achievement he received an academic scholarship to the University of Chicago, where he studied mathematics, physics, chemistry, and astronomy. During the summer, Hubble tutored and worked to earn money for his college expenses. In his junior year he received a scholarship in physics, and by his senior year he was working as a laboratory assistant to physicist Robert A. Millikan.
Hubble graduated in 1910 with a bachelor's degree in mathematics and astronomy. In addition to pursuing an academic career, the six-foot two-inch Hubble was an amateur heavyweight boxer. According to one unconfirmed story, sports promoters urged him to become a professional boxer and fight against heavyweight champion Jack Johnson, an offer Hubble declined.
Starts out as lawyer
Upon receiving a Rhodes Scholarship in 1910, Hubble attended Queen's College at the University of Oxford in England. He studied jurisprudence (the science or philosophy of law), completing the two-year course in 1912, then began work toward a bachelor's degree in law. Eventually he changed his major to Spanish. While at Oxford Hubble also continued his athletic endeavors, excelling in the high jump, broad jump, shot put, and running. In 1913, he returned to the United States and began practicing law in Louisville, Kentucky, where his family was living. Bored with his law career within a year, Hubble returned to the University of Chicago to work toward a doctorate in astronomy at the Yerkes Observatory.
Begins life's work
At the time Hubble attended the University of Chicago, the Yerkes Observatory was a waning institution that did not actually offer formal courses in astronomy. Working under the supervision of Edwin B. Frost, the observatory's director, however, Hubble made regular observations on the Yerkes telescope and studied on his own. Hubble's work at this time was reportedly influenced by a lecture he attended at Northwestern University in Chicago. At the presentation, Lowell Observatory astronomer Vesto M. Slipher presented evidence that spiral nebulae (in that era, the term nebulae was used to describe any celestial body not obviously identifiable as a star) had high radial velocities (the velocities at which objects appear to be moving toward or away from Earth in a direct line of sight). Slipher had found spiral nebulae that were moving at much higher velocities than stars generally moved, thus suggesting that the nebulae might not be part of the Milky Way.
During his term at Yerkes, Hubble also met astronomer George E. Hale, founder of the Yerkes Observatory and then the director of Mount Wilson Observatory in Pasadena, California. In 1916, Hale invited Hubble to join the Mount Wilson staff once he received his doctorate. Hubble's acceptance of this offer was delayed by World War I (1914-18), however. He joined the army in 1917, attaining the rank of major before being wounded in battle. After his discharge in 1917 he began work at Mount Wilson. The observatory had two telescopes, a 60-inch reflector and a newly operational 100-inch reflector, the largest in the world at that time. (In a reflector telescope light passes down an open tube then hits a curved mirror at the lower end that reflects the light back up the tube, directing it onto a smaller mirror that again reflects the light into the eyepiece.) Hubble would remain at Mount Wilson for his entire career.
Discovers new galaxies
Hubble's first notable achievement at Mount Wilson was the confirmation of the existence of galaxies outside the Milky Way. From observations he made in October 1923, Hubble was able to identify a type of variable star known as a Cepheid (pronounced SEF-ee-id) in the Andromeda nebula (known today as the Andromeda galaxy). (Variable stars got their name because their light output changes over time, varying between dim and bright.) By using information about the relationship between brightness, luminosity (how much light a star radiates), and the distances of Cepheid stars in Earth's galaxy, Hubble was able to estimate the distance to the Cepheid in the Andromeda nebula to be about one million light-years. (A light-year measures the distance light travels in a year, about six trillion miles).
Hubble also discovered other Cepheids, as well as other objects, and calculated the distances to them. Since scientists knew that the maximum diameter of the Milky Way was only 100,000 light-years, Hubble's figures established the existence of galaxies outside our own. Eventually he discovered nine new galaxies. Consistent with scientific terminology of his time, Hubble called the galaxies "extragalactic nebulae." The results of Hubble's work were publicly announced at the December 1924 meeting of the American Astronomical Society, settling one of the great scientific debates of that era, that galaxies other than the Milky Way did exist. In 1924, Hubble also married Grace Burke Leib.
Introduces galaxy classification system
In 1925, having proved the existence of galaxies beyond our own, Hubble introduced a system of classifying them, or breaking them down into types of galaxies. Most he divided into two main groups, regular or irregular. In addition, regular galaxies were either spiral or elliptical. Spiral galaxies, like the Milky Way, have huge arms of new stars that trail around a rotating center of older stars. The elliptical galaxies also rotate around a center of older stars, but they are shaped like saucers, lacking the new-star arms of the spiral galaxies. The system used to classify galaxies today is still based on Hubble's structure.
Uses redshifts to determine distances
Hubble continued his pioneering work on galaxies throughout the 1920s, determining distances for over twenty galaxies surrounding the Milky Way. In 1929, this work led to his most important discovery. For over a decade, scientists--including Slipher--had predicted that the light coming from some distant galaxies might indicate that the galaxies were moving apart from each other and Earth. If the galaxies were speeding fast enough away from Earth, the motion would "stretch" the light waves emitting from them. Since longer wavelengths make light take on a reddish tone, this stretching was called the "redshift."
The mathematics for predicting redshifts were based on the general theory of relativity, published in 1916 by physicist Albert Einstein and extended in the 1920s by other mathematicians. General relativity held that gravity is not so much a force as it is geometry--the geometry of space. Big objects like planets bend the space around them; smaller objects simply follow the bending of space.
Formulates Hubble's law
Hubble's greatest achievement was to determine the redshifts for a large number of galaxies by measuring the wavelengths of the light coming from them. His measurements led him to two important conclusions. First, distant galaxies did seem to be moving away from Earth. Second, the farther away they were from Earth, the faster they seemed to move. This relationship, between a galaxy's distance and its speed, is now known as Hubble's law.
At first glance, this observation of the movement of galaxies relative to Earth might make it seem that Earth was somehow the center of the universe. Instead, though, the motion of the galaxies can be explained by an idea based on Einstein's theory of relativity: the expansion of space itself. It is not so much that the galaxies are moving by themselves, according to this idea; rather, they are moving along with the expanding space around them.
Arrives at proof of big bang
Thanks to Hubble's observations, scientists now had a way of starting to answer the seemingly unanswerable question of how old the universe is and how it began. If the universe were expanding, they figured, that expansion had to start somewhere. Aleksandr Friedman and Georges Lemaître, two mathematicians who had extended Einstein's work in the 1920s, had found that relativity suggested an origin for the universe. That origin, they said, was a single point from which the universe had first expanded. From this tiny point, known as a singularity, space, time, and matter (or material substance; virtually everything in the universe is made up of matter) expanded into being.
This idea was highly controversial. Leading cosmologists argued against it. They suggested instead that the universe exists in a steady state, without beginning or end, in which expansion comes from the constant creation of new matter. Taking the position opposite the steady-staters were scientists like George Gamow, who came up with the term big bang in 1946 to describe the universe's earliest expansion.
Hubble himself stayed out of such cosmological arguments. Dignified and gentlemanly, he puffed a pipe and spoke with a slight British accent picked up in his three years at Oxford. He viewed his role as simply one of observing and reporting what he observed. For example, he described the galaxies as only appearing to be moving according to his measurements. He left it to others to claim that that was what they were actually doing.
Becomes associated with Mount Palomar
By the 1930s, Hubble had firmly established himself as America's leading astronomer. He was now in charge of the Mount Wilson Observatory, a father figure to a whole generation of astronomers who studied there. They read his books and articles, including his volume about galaxies, The Realm of the Nebulae (1936). Many of them imitated his way of talking and manner.
During the 1930s and 1940s, Hubble was closely involved in the planning and construction of a new 200-inch telescope at Mount Palomar, another Southern California observatory not far from Mount Wilson. It was called the Hale telescope, after Hubble's mentor at Mount Wilson, George E. Hale. During World War II (1939-45), Hubble worked for the army as the head of a research department, and in 1948, when the Hale telescope was completed, he was the first to use it.
Despite suffering from heart disease in the last years of his life, Hubble continued to work at Mount Wilson and Mount Palomar. He died on September 28, 1953, of a cerebral thrombosis (a type of stroke) while preparing for a four-day observation on Mount Palomar.
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