Edwin Hubble

Edwin Powell Hubble was born on November 20, 1889, in Marshfield, Missouri, one of several children of John Powell Hubble, an insurance executive, and Virginia Lee James Hubble ^[1]. The family moved to Wheaton, Illinois, near Chicago, while Edwin was still a boy, and it was there that he passed most of his school years. He was a strong student, but classmates and teachers remembered him first as an athlete. He ran track, played basketball, and set a state high school record in the high jump ^[2].

Hubble entered the University of Chicago in 1906, where he studied mathematics, astronomy, and physics while continuing to compete in sports. He worked for a time as a laboratory assistant to the physicist Robert Millikan, who would later win a Nobel Prize ^[1]. In 1910 Hubble won a Rhodes Scholarship to Oxford. His father wanted him to pursue a respectable profession rather than science, so at Oxford he read jurisprudence, adding literature and Spanish, and he absorbed English manners and dress that he kept for the rest of his life, including a pipe, tweeds, and a cultivated accent that amused some American colleagues ^[2].

He returned to the United States in 1913, shortly after his father's death. For about a year he taught Spanish, physics, and mathematics at a high school in New Albany, Indiana, where he also coached basketball, and he was admitted to the Kentucky bar although he appears never to have built a legal practice ^[1]. Astronomy kept pulling at him. In 1914 he went back to the University of Chicago as a graduate student at Yerkes Observatory in Wisconsin, completing a doctoral thesis in 1917 on photographic investigations of faint nebulae, the very objects that would define his career ^[3].

George Ellery Hale, the founder and director of Mount Wilson Observatory near Pasadena, offered Hubble a staff position as he finished his doctorate. The United States had just entered the First World War, and Hubble reportedly telegraphed his acceptance but enlisted in the Army first. He served with the 86th Division, rose to the rank of major, and reached France near the end of the fighting, though he saw no combat ^[2]. He joined Mount Wilson in 1919, arriving just as the observatory's 100-inch Hooker telescope, then the most powerful in the world, came into full operation ^[1].

The timing could hardly have been better. Astronomy in 1920 was divided over a basic question: were the spiral nebulae, faint pinwheel-shaped smudges scattered across the sky, relatively small clouds inside the Milky Way, or were they separate stellar systems, so-called island universes, at enormous distances? The dispute was aired publicly in the famous 1920 debate between Harlow Shapley and Heber Curtis at the National Academy of Sciences, and it remained unsettled because nobody could measure how far away the nebulae were ^[4].

Hubble attacked the problem with the Hooker telescope's unmatched light-gathering power. In October 1923 he found a Cepheid variable star in the Andromeda nebula, M31. Cepheids pulse with a period tied to their true brightness, a relationship worked out by Henrietta Swan Leavitt, which makes them usable as distance markers ^[4]. Hubble's Cepheid gave a distance for Andromeda of roughly a million light years, far beyond any estimate of the Milky Way's size. The nebula had to be a galaxy in its own right. The result was announced at a meeting of the American Astronomical Society in January 1925, and the island universe question was effectively closed ^[3].

Any list of Edwin Hubble achievements begins with that 1923 to 1925 proof that galaxies exist beyond our own, but his second great discovery reshaped physics even more deeply. Vesto Slipher at Lowell Observatory had shown years earlier that the light of most spiral nebulae is shifted toward the red end of the spectrum, implying motion away from Earth ^[5]. Hubble, working with the gifted Mount Wilson assistant Milton Humason, combined those velocity measurements with his own painstaking distance estimates for the same galaxies.

In 1929 Hubble published a short paper showing a roughly linear relation: the farther away a galaxy lies, the faster it recedes ^[6]. Humason then measured redshifts for much fainter, more distant galaxies, and a joint paper in 1931 extended and strengthened the relation. This velocity-distance rule became known as the Hubble law, and its constant of proportionality as the Hubble constant. Interpreted through general relativity, it meant space itself is expanding, exactly the behavior Georges Lemaitre had proposed theoretically in 1927 ^[5]. Albert Einstein, who had modified his own equations to keep the universe static, visited Mount Wilson in 1931 and abandoned that modification in light of the observations ^[2].

Hubble's early value for the constant, near 500 kilometers per second per megaparsec, was far too high because of errors in the Cepheid distance scale that were corrected by later astronomers, but the linear relation itself has held for nearly a century ^[4]. Alongside these discoveries, Hubble created a classification scheme for galaxies, sorting them into ellipticals, spirals, and barred spirals in a sequence still called the Hubble tuning fork, and he published influential summaries of the new extragalactic science, most notably his 1936 book The Realm of the Nebulae ^[3].

In 1924 Hubble married Grace Burke Leib, the widowed daughter of a Los Angeles banker. The couple had no children and settled in San Marino, close to the observatory offices in Pasadena. Grace kept detailed journals of their life together, and those notebooks became a major source for later biographers, though scholars have noted that they present her husband in a carefully polished light ^[2].

The Hubbles moved comfortably in Southern California society. Their circle included writers, musicians, and Hollywood figures, and visitors such as Aldous Huxley and Igor Stravinsky appeared at their dinner table. Hubble enjoyed fly fishing, collected old books on the history of science, and cultivated the reserved, formal persona he had adopted at Oxford ^[2]. Colleagues found him variously impressive and distant. He was famous to the public in a way few astronomers have been, appearing on the cover of Time magazine and guiding celebrities around Mount Wilson ^[1].

Biographers, most thoroughly Gale Christianson, have documented that Hubble embroidered parts of his own life story, including tales of wartime exploits and legal practice that the record does not support ^[2]. Such findings complicate the man without diminishing the discoveries. The observational work was checked, extended, and confirmed by others, and it stands on its own.

During the Second World War Hubble left astronomy to serve as chief of ballistics at the Aberdeen Proving Ground in Maryland, where he directed work on the behavior of projectiles and was awarded the Medal for Merit in 1946 ^[1]. He returned to Mount Wilson after the war and threw his influence behind the completion of the 200-inch Hale telescope on Palomar Mountain, a project delayed by the conflict.

When the giant instrument was dedicated in 1948, Hubble was given the honor of using it first, photographing a faint nebulosity as its opening scientific exposure ^[3]. He planned an ambitious program to push measurements of the galaxy redshift relation to far greater depths, hoping the new telescope would reveal whether the expansion was slowing. A heart attack in 1949, suffered while on vacation in Colorado, forced him to reduce his workload, though he continued observing on a lighter schedule with help from Humason and the younger astronomer Allan Sandage, who inherited the distance-scale program ^[2].

Hubble died suddenly of a cerebral thrombosis on September 28, 1953, in San Marino, California, at the age of 63 ^[1]. At Grace Hubble's wish there was no funeral, and the location of his remains was never made public. He never received a Nobel Prize; the physics prize did not then recognize astronomical work, although committee records later suggested he had been under serious consideration near the end of his life ^[4].

Few scientists have a stronger claim to founding a discipline. Observational cosmology, the study of the universe as a whole through measurement rather than speculation, dates in practice from Hubble's distance work of the 1920s. The expansion he documented became the first pillar of Big Bang cosmology, and the number that carries his name, the Hubble constant, remains one of the most intensely measured quantities in science. Its precise value is still debated today, a discrepancy known as the Hubble tension, which keeps his name in current research papers nearly a century after the 1929 result ^[5].

His name is attached to the Hubble Space Telescope, launched by NASA in 1990, which has orbited Earth for decades and produced some of the most widely reproduced astronomical images ever made. The choice of name was deliberate: an instrument built to measure the distances and expansion rate of galaxies honored the man who first showed such measurements were possible ^[7]. In 2018 the International Astronomical Union voted to rename the expansion law the Hubble-Lemaitre law, acknowledging Lemaitre's earlier theoretical derivation while keeping Hubble's observational contribution in the title ^[8].

Edwin Hubble facts now sit in every introductory astronomy course: the proof that Andromeda is a separate galaxy, the tuning fork classification, the velocity-distance law. Craters on the Moon and Mars, an asteroid, and his Missouri birthplace museum all carry his name. Any honest Edwin Hubble biography must weigh the self-mythologizing against the science, but the central fact is untouched: he found the scale of the universe, and then he found that it is growing ^[2].