Edwin Hubble: The Pioneer of Distant Stars Spectra Magazine

Edwin Powell Hubble was born on November 20, 1889, in Missouri, US. He was the son of a businessman named John Hubble who worked in the insurance industry; his mother, Virginia James, was a homemaker. He was a bright student and in 1906 won a scholarship to the University of Chicago, Illinois, where he studied philosophy, mathematics, and astronomy. There he served as a lab assistant for a year for Robert Millikan, an American physicist who won the Nobel prize in Physics for the measurement of electric charge. Hubble graduated in 1910. Afterwards, he went to Oxford University in 1911 after being awarded a Rhodes scholarship to study law and Spanish. He had taken these subjects at the insistence of his father. In 1913, after getting his degree, he taught at a high school in Indiana. After the death of his father, he was free to pursue a scientific career. Therefore, in 1913, he went to the University of Chicago once again to graduate in astronomy. In February 1924, he married Grace Burke Leib; they had no children.

Career

He conducted his research at the Yerkes Observatory in Williams Bay, Wisconsin, under the supervision of the astronomer Edwin Frost. It was Hubble’s luck that he was completing his studies just as the director of Mount Wilson, George Hale was hiring new staff. He was offered a job, and he accepted it; however, before he could take up the position there, the US started a war with Germany on April 6, 1917. He delayed joining the observatory to enlist in the US Army; however, Hale kept the position open for him until the end of the war.

Hubble enlisted in the US Army. Image source: Wikimedia

In 1919, he joined the astronomy establishment, and with the Hooker telescope — the most advanced telescope of that time — he was able to look at the sky with more detail. He initially studied the reflection nebulae within the Milky Way. Soon, he returned to the problem of ‘spiral nebulae’, the same objects he had investigated for his doctorate. The status of the spirals was then unclear: were they ‘distant stars’ (currently known as galaxies), just clouds of gas or clusters of stars? The answer to this was soon provided by Hubble.

In 1923, Hubble spotted a Cepheid Variable star in the Andromeda Nebula. The fluctuations in the light of these stars allowed Hubble to determine the nebula’s distance through the relation between the period of Cepheid fluctuations and its luminosity. Hubble’s estimate laid the Nebula approximately 900,000 lightyears away and placed it beyond the borders of the Milky Way. In 1924, Hubble proved through the paper ‘Cepheid in Spiral Nebula’ that more galaxies existed. Before this discovery, it was thought that the Milky Way is the only galaxy present in the universe.

Cepheid Variable star. *Image source: Wikimedia*

Within a few years of this groundbreaking research, Hubble decided to go on another adventure. He decided to find the answer to the question of why the vast majority of galaxies seem to be moving away from the Earth. To tackle this question, Hubble worked with another Mount Wilson astronomer, Milton Humason. Humason measured the spectral shifts of the galaxies while Hubble worked on determining their distances. In 1929, he published his first paper on the relationship between redshift and distance. He concluded that they share a linear relationship, that is if one galaxy is twice as far away as another, its redshift will be twice as large. After two years, Humason and Hubble presented what astronomers and cosmologists deemed as convincing evidence that the relationship between redshift and distance is indeed linear and that redshift is directly proportional to its distance.

Later Life

Hubble ran the Mount Wilson Observatory for the rest of his life. He worked day and night to get astronomy recognized by the Nobel Prize Committee. During World War II, he served in an administrative capacity at the Aberdeen Proving Grounds in Maryland. He also worked on the Hale telescope — a 200-inch reflecting telescope at the Palomar Observatory in California, US, named after the astronomer and director of Mount Wilson George Ellery Hale. In 1953, at the age of 70, Hubble died as a result of cerebral thrombosis.