🇺🇸Edwin
Hubble

On the night of October 5, 1923, Edwin Hubble positioned the 100-inch Hooker Telescope on Mount Wilson toward a fuzzy patch of light in the constellation Andromeda. What he found there — a single variable star of a type whose brightness cycle reveals its true distance — would collapse the known universe and replace it with something incomparably larger. By measuring the star's fluctuations against its apparent brightness, Hubble calculated that the Andromeda Nebula lay nearly a million light-years away. The Milky Way, at the time believed to contain the entire cosmos, stretches only about one hundred thousand light-years across. Andromeda was not a cloud within our galaxy. It was a galaxy in its own right. The universe was not one island of stars. It was an ocean of islands, and Hubble had just found the shore of one of them.

Edwin Powell Hubble was born on November 20, 1889, in Marshfield, Missouri, and grew up in Wheaton, Illinois. He was a capable athlete — good enough at boxing that promoters tried to arrange a match against the world heavyweight champion Jack Johnson — and a gifted student who won a scholarship to the University of Chicago, where he studied mathematics and astronomy under the great George Ellery Hale. His father, a lawyer, exacted a deathbed promise from his son to study law before taking up science. Hubble honored it, earning a law degree at Oxford on a Rhodes Scholarship, briefly practicing law in Kentucky, then abandoning it entirely for astronomy. By 1919 he had joined the staff of the Mount Wilson Observatory in California, home to the most powerful telescope on earth. He was thirty years old, and he had found his instrument.

The question that animated Hubble's early career was one of the great unsettled controversies of the era: the nature of the spiral nebulae. Some astronomers argued they were distant star systems — "island universes" analogous to the Milky Way, a concept first proposed by Immanuel Kant in 1755. Others maintained they were relatively nearby gas clouds within our own galaxy. The dispute could not be resolved without measuring the nebulae's distances, and distances at cosmological scales required a reliable standard candle — a class of object whose intrinsic brightness was known, so that its apparent dimness in the sky could be converted into a distance. Hubble found it in Cepheid variable stars, whose period of brightness oscillation had been linked to absolute luminosity by Henrietta Swan Leavitt in 1912. The Cepheid in Andromeda settled the argument permanently.

But Hubble was not finished. In 1929, synthesizing his own measurements of galactic distances with velocity data gathered by his colleague Milton Humason and earlier work by Vesto Slipher, Hubble published a paper announcing a relationship that would become the foundation of modern cosmology: the farther a galaxy, the faster it recedes. The recessional velocities of galaxies were proportional to their distances, with a constant of proportionality now known as the Hubble constant. This was not merely an observational curiosity. It meant the universe was expanding — that every galaxy was moving away from every other, like dots on the surface of an inflating balloon. Running the expansion backward implied that all matter had once been concentrated at a single point. It implied, in other words, what Georges Lemaître had already proposed theoretically: a beginning. What we now call the Big Bang.

Hubble spent the remainder of his career at Mount Wilson and at the Palomar Observatory, where the 200-inch Hale Telescope — the largest in the world — came online in 1948. He was nominated for the Nobel Prize in Physics but died before the committee acted; at the time, the prize was not awarded posthumously, and the Nobel Committee had not yet recognized astronomy as a category of physics. He died on September 28, 1953, of a cerebral thrombosis. In 1990, NASA launched the Hubble Space Telescope, named in his honor, which has since produced imagery of the cosmos that has permanently altered humanity's sense of its own scale and place within creation.