Edwin Hubble, for whom the Hubble Space Telescope is named, was one of the leading astronomers of the twentieth century. His discovery in the 1920s that countless galaxies exist beyond our own Milky Way galaxy revolutionized our understanding of the universe and our place within it.
Hubble, a tall and athletic man who excelled at sports and even coached high school basketball for a short while, started his professional science career during one of the most exciting eras of astronomy. It was 1919, just a few years after Albert Einstein published his theory of general relativity, and bold, new ideas about the universe were fermenting. Hubble was offered a staff position at the Mount Wilson Observatory, which housed the newly commissioned 100-inch Hooker telescope, then the largest telescope in the world. Hubble, it seemed, had the universe placed in his lap.
Most astronomers of Hubble's day thought that all of the universe — the planets, the stars seen with the naked eye and with powerful telescopes, and fuzzy objects called nebulae — was contained within the Milky Way galaxy. Our galaxy, it was thought, was synonymous with the universe.
In 1923 Hubble trained the Hooker telescope on a hazy patch of sky called the Andromeda Nebula. 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 1920s, 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. Several scientists had also posed this theory based on Einstein’s General Relativity, but Hubble's data, published in 1929, helped convince the scientific community.
Hubble and his colleague at Mt. Wilson, Milton Humason (who started as a mule driver during the construction of the observatory, then janitor, then night assistant), estimated the expansion rate of the universe to be 500 kilometers per second per megaparsec. (A megaparsec, or a million parsecs, is a distance equal to about 3.26 million light-years; so a galaxy two megaparsecs away is receding from us twice as fast as a galaxy only one megaparsec away.) This estimate is called the Hubble Constant, and scientists have been fine-tuning it ever since.
The Hubble Space Telescope was launched in 1990, one of its major goals being to pin down the Hubble Constant. In 2001, a team studying supernovae with Hubble, along with ground-based optical telescopes, established a rate of 72 ± 8 km/sec/Mpc. In 2006, a team studying the cosmic microwave background with NASA's WMAP satellite tweaked this measurement to 70 km/sec/Mpc. Hubble, the telescope, also helped discover that not only is the universe expanding, the expansion is accelerating. The mysterious force causing this acceleration is dubbed dark energy.
Hubble was born on November 20, 1889, in Marshfield, Missouri, and moved to Wheaton, Illinois, before his first birthday. He studied mathematics and astronomy at the University of Chicago and earned a bachelor of science degree in 1910. He was one of the first Rhodes Scholars at Oxford University, where he studied law. After serving briefly in World War I, he returned to the University of Chicago and earned his doctorate degree in 1917. After a long career entirely at Mt. Wilson Observatory, he died of a heart attack on September 28, 1953, in San Marino, California. As with the telescope that bears his name, Edwin Hubble transformed our understanding of the universe. His spirit of discovery lives on today in the Hubble Space Telescope.