Edwin Hubble

Edwin Hubble the American astronomer (1889-1953) whose observations of distant galaxies transformed the modern picture of the universe. He demonstrated that the cosmos extends far beyond the Milky Way, provided the first observational evidence that it is expanding, and gave his name to the law relating a galaxy's distance to its recession velocity and to the orbiting space telescope launched in 1990.

Early Life and Education

Edwin Powell Hubble was born on 20 November 1889 in Marshfield, Missouri, the son of an insurance executive, and grew up in Wheaton, Illinois. He was a gifted student and a talented athlete, and he captained the University of Chicago basketball team while earning a bachelor's degree in mathematics and astronomy in 1910. He then travelled to England as a Rhodes scholar at Queen's College, Oxford, where he studied jurisprudence and later literature, a detour that left him with the polished manner and wide culture for which colleagues remembered him.

He returned to the United States and taught high school in Indiana for a year before deciding to make astronomy his career. He entered the University of Chicago again, completed a doctoral dissertation on photographic investigations of faint nebulae in 1917, and then served in the United States Army during the First World War, rising to the rank of major. After the war he joined the staff of the Mount Wilson Observatory in California, where the great hundred-inch Hooker telescope awaited him.

Galaxies Beyond the Milky Way

When Hubble began observing, most astronomers believed that the spiral nebulae were clouds of gas within our own galaxy, the Milky Way, which many assumed to be the whole of the universe. Using the new hundred-inch telescope, Hubble identified Cepheid variable stars in the Andromeda nebula and applied the period-luminosity relation established by Henrietta Swan Leavitt to estimate their distance. The result placed Andromeda far outside the Milky Way, proving that it was a separate galaxy.

He went on to find Cepheids in other spiral nebulae, and the distances he measured left no doubt that the universe is populated by countless galaxies like our own. This discovery of the extragalactic universe, announced in the early 1920s, ended the long debate over the scale of the cosmos and established the Milky Way as one galaxy among vast numbers. It was one of the decisive observational advances of twentieth-century astronomy.

The Expanding Universe

Hubble combined his own distance measurements with the redshifts that Vesto Slipher and others had measured in the spectra of galaxies. He found that the farther a galaxy lies from us, the faster it appears to recede, a linear relationship now known as Hubble's law and expressed through the constant that bears his name. The paper announcing this result in 1929 provided the observational foundation for the idea of an expanding universe.

The interpretation of the redshifts as a general expansion had been anticipated theoretically by Georges Lemaitre, and the observations gave the theory decisive support. Hubble himself was cautious about the cosmological conclusion, preferring to describe the phenomenon as an apparent relation between redshift and distance, but the pattern he established became the cornerstone of modern cosmology and the starting point for estimates of the age of the universe.

Classification and the Nature of Galaxies

Hubble devised a morphological classification of galaxies that organized them into ellipticals, spirals and barred spirals, and an irregular class. Arranged in the diagram he drew, the sequence became known as the tuning fork, and it is still the foundation of galaxy classification. His scheme provided a common language for describing the shapes and structures of the immense systems he had shown to lie beyond our own.

He also studied the distribution of galaxies and their clustering, and he examined the diffuse luminosity of the night sky. His work helped to establish that galaxies are the basic building blocks of the large-scale universe and that they are distributed in groups and clusters. These studies framed the questions about cosmic structure that later generations of astronomers would pursue with new instruments.

Influence and Legacy

Hubble's discoveries reshaped both astronomy and cosmology, turning the universe from a single galaxy into an expanding realm of innumerable galaxies. His name is attached to the law of cosmic expansion, to the constant that measures its rate, and to the space telescope that since 1990 has carried his legacy into orbit, returning images of distant galaxies that refined the very measurements he pioneered.

He received many honours, including election to the Royal Society and the presidency of the American Astronomical Society, and he worked at Mount Wilson until his death in 1953 at San Marino, California. Some felt he deserved a Nobel Prize, but the award then recognized no work in astronomy, a limitation later remedied. He is remembered as the observer who first revealed the scale and motion of the universe.

See also

• Hubble's law
• Andromeda Galaxy
• Cosmic distance ladder
• Mount Wilson Observatory