What Did Edwin Hubble Discover? The Astronomer Who Made the Universe Bigger

Edwin Hubble (1889–1953) made two discoveries that changed how we picture the cosmos. First, using special pulsating stars, he showed in 1924 that spiral "nebulae" such as Andromeda are not clouds inside our Milky Way but entire galaxies far beyond it. Second, in 1929 he found that the farther away a galaxy is, the faster it is moving away from us, a relationship that implies the universe is expanding. In a few years, the known universe went from one galaxy to countless galaxies, and from static to growing.

A lawyer who preferred the stars

Hubble was born in 1889 in Marshfield, Missouri. He was a gifted athlete as well as a student, and after graduating from the University of Chicago he went to Oxford as a Rhodes Scholar, where he studied jurisprudence. Law did not hold him for long. He returned to astronomy and completed a Ph.D. at Yerkes Observatory in 1921. He also served in the U.S. Army during the First World War, rising to the rank of major, although his unit never saw combat.

Mount Wilson and the biggest telescope

In 1919 Hubble joined the staff of Mount Wilson Observatory in California, where he would work for the rest of his life. The observatory had the newly completed 100-inch Hooker telescope, then the most powerful in the world. It was the right instrument at the right moment.

The Great Debate: how big is the universe?

In the early 1920s astronomers argued about the nature of the fuzzy spiral "nebulae" visible in telescopes. Were they gas clouds within our own galaxy, or "island universes", separate galaxies at enormous distances? There was no reliable way to measure how far away they were.

Measuring distance with blinking stars

The key was a type of star called a Cepheid variable. Cepheids brighten and dim in a regular rhythm, and the length of that cycle is linked to how bright the star really is. If you know a star's true brightness and see how faint it looks, you can calculate its distance, just as a car's headlights look dimmer the farther away the car is.

Using the Hooker telescope, Hubble found Cepheid variables in the Andromeda nebula and in other spirals. The distances they implied were far too great for these objects to be inside the Milky Way. They were galaxies in their own right. His results were reported in The New York Times in November 1924. Overnight, our galaxy became one among many.

Sorting galaxies

Hubble then set about organising this new universe. He created a classification system for galaxies based on their appearance, separating them into elliptical, spiral and barred spiral types, often drawn as a "tuning fork" diagram. The Hubble sequence is still the most widely used system for classifying galaxies.

1929: the galaxies are rushing away

Earlier, the astronomer Vesto Slipher had measured that the light from many galaxies was shifted towards the red, meaning they were moving away from us. Hubble combined such velocity measurements with his own distance estimates and found a striking pattern: the farther a galaxy is, the faster it recedes.

This relationship is now known as Hubble's law, or the Hubble–Lemaître law, because the Belgian physicist and priest Georges Lemaître had proposed it two years earlier. Its meaning is profound: the universe is expanding. Run that expansion backwards in time, and you arrive at the idea of a hot, dense beginning, what we now call the Big Bang.

Hubble's own estimate of the expansion rate was about 500 kilometres per second per megaparsec, far higher than modern values of roughly 68–74, because of errors in the calibration of his distances. Science corrected the number; the discovery stood.

No Nobel, but a telescope

Astronomy was not then treated as part of physics for the Nobel Prize, and Hubble lobbied to change that. The change came, but not in his lifetime. He died in 1953 in San Marino, California.

His name lives on in the Hubble Space Telescope, which has shown us galaxies far beyond anything he could see. It is a fitting tribute to the man who first showed that our galaxy is just one of very many.

Learn with Hubble: English phrases about discovery

Phrase	Meaning	Example
to broaden your horizons	to experience or learn new things	Learning Spanish broadened my horizons.
a whole new world	a completely new area of experience	Reading in English opened a whole new world.
the bigger picture	the overall situation	Don't worry about one mistake; look at the bigger picture.
light years ahead	far more advanced	Her pronunciation is light years ahead of mine.
to keep an open mind	to be willing to consider new ideas	Keep an open mind about new methods.

Try this: Hubble discovered that our galaxy is one of many. Write three English sentences about a moment when learning a language showed you "a whole new world", using "broaden your horizons" and "the bigger picture".