Edwin Hubble Biography

World of Scientific Discovery on Edwin Hubble

Edwin Hubble, born in Marshfield, Missouri, on November 20, 1889, made as great an impact on the astronomy of the twentieth century as Nicholas Copernicus did in the sixteenth century. At the time of Hubble's birth, no galaxies outside our own were known to exist. His work increased the scale of the known universe a billion-fold.

Hubble attended the University of Chicago where he was influenced by physicist Robert A. Millikan and astronomer George Hale (1868-1939). After receiving a degree in mathematics and astronomy, Hubble went to Oxford University in England where he studied law. He returned to the United States in 1923 and opened a law office in Louisville, Kentucky. This career evidently was not fulfilling, for in 1914, he returned to the University of Chicago to work at the Yerkes Observatory where he made a meticulous study of the mysterious fuzzy patches of light called nebulae.

The nature of these nebulae was as yet unclear. Were they small bodies within our own galaxy, or were they much larger and more distant? Heber D. Curtis (1872-1942) believed they were "island-universes," external to the galaxy, while others, such as Harlow Shapley, preferred to ride the fence until someone found irrefutable proof.

Hubble concluded that the planetary nebulae (so named because they look like the disc of a planet through a telescope) are a part of our galaxy, while spiral nebulae are outside it. He admitted that additional studies with more powerful telescopes would be needed before his conclusions could be determined with absolute certainty, but the groundbreaking work was enough to earn him his Ph.D.

Hale learned of Hubble's competence as an observer and offered him a position at the Mount Wilson Observatory, soon to be the home of the largest telescope on earth. Following service in World War I, Hubble accepted.

Hubble arrived at Mount Palomar as the 100-inch (2.5 meter) telescope became operational, and he used it to continue studying the nebulae. On October 5, 1923, he identified a special type of star, called a Cepheid variable star, in a photograph of the great nebula in Andromeda. Henrietta Leavitt and Shapley had discovered they could use Cepheids to measure distance, and Hubble made use of their work. At the end of 1924, when he had identified twelve Cepheids, Hubble was able to determine that the distance to the Andromeda nebula was 900,000 light years. It was definitely not a part of our galaxy; it was far more enormous and distant. It had been revealed as a galaxy!

The result of this announcement was staggering. Just as Copernicus had dethroned the earth from the center of the solar system, Hubble took significance away from the Milky Way galaxy. It became just one average-sized star system in a sea of uncounted galaxies.

Hubble studied all the galaxies he could find. He noticed they could be grouped into two main classes: spiral and elliptical. In addition to establishing a modern system of classifying galaxies, he studied their distribution and motion, finding they were uniformly located through space. By 1929 he had determined distances for 22 galaxies in Virgo.

With this information he devised what became known as Hubble's law, which states that the rate at which a galaxy appears to be receding from us is directly proportional to its distance. The constant of propotionality between these two quantities is called the Hubble constant, and determining its value is one of the formost problems in modern astronomy. The units of the Hubble constant are kilometers per second per megaparsec (one megaparsec equals 1,000,000 parsec, or 3,262,000 light years). Some research groups have determined a value of about 100 for the Hubble constant. This means that a galaxy one megaparsec away would be receding at 100 kilometers per second, a galaxy 10 megaparsecs away would be receding at 1,000 kilometers per second, and so on. However, other researchers have obtained values closer to 50 for the Hubble constant, which implies slower expansion, and therefore greater age, of the Universe. Detailed investigations in the 1990s have settled on values closer to 85, but as of the late 1990s, this basic problem of cosmology remains unsolved.

The Hubble law became the most important of all Hubble' discoveries. This law made it possible to relate a galaxy's distance to the red shift of its light. Milton Humason, Hubble's colleague, photographed the distant galaxies and studied their spectra. Because the spectra were red shifted, it was obvious the galaxies were moving away, and the amount of red shift indicated how fast they were traveling. Humason found some were cruising at about one-seventh the speed of light!

The implications of this discovery were enormous. What was responsible for this incredible velocity? From what point were the galaxies all rushing? Hubble suggested that at some time in the distant past, which he estimated at two billion years, all the matter in the universe was densely packed in one place. His observational evidence provided the link between the theories of Albert Einstein and the cosmic egg hypothesis of Georges Henri Lemaître, giving birth to modern cosmology.

In 1949 the 200-inch (5 meter) telescope went into operation at Mount Palomar. Hubble was the first to use it, but the first major discovery there was made by Walter Baade. In 1952, after conducting a study of Cepheids in the Andromeda galaxy, Baade realized Hubble's estimate of Andromeda's distance had been in error. Andromeda was actually twice as far away as Hubble had thought! Since this distance had been used as a yardstick by astronomers to calculate time and distance, Baade concluded that not only was the universe much larger, but that the big bang had probably occurred 20 billion, not two billion, years in the past.

During this time, Hubble's health had been deteriorating because of a heart ailment. On September 28, 1953, while planning to go to Mount Palomar for four nights of observing, the 64-year-old man who had changed the size and scope of the universe suffered a cerebral thrombosis and died.