Edwin Hubble

Who Made the Universe Much Larger · Astronomer · 1889–1953

The Mount Wilson observer who proved that the faint spiral nebulae are other galaxies, then showed that the further away a galaxy is, the faster it is receding from us.

Who was Hubble?

Edwin Powell Hubble was born in Missouri in 1889, boxed as a heavyweight, won a Rhodes Scholarship, and read law at Oxford to please his father before returning to astronomy as soon as he decently could. He also acquired at Oxford an English accent and manner he never afterwards dropped. In 1923, using the 100-inch telescope on Mount Wilson — then the largest in the world — he identified a Cepheid variable star in the Andromeda nebula. Cepheids announce their true brightness through the period of their pulsation, a relationship discovered by Henrietta Swan Leavitt, so comparing the true brightness with the observed faintness gives the distance. The distance was vast: Andromeda was not a cloud within the Milky Way but a galaxy of its own, and the universe was suddenly enormously larger than anyone had supposed. Working with Milton Humason, who had arrived at the observatory as a mule driver and janitor and who took most of the spectra, Hubble then plotted the red-shifts of galaxies against their distances. The points lay on a straight line: recession speed is proportional to distance. That is not an explosion with us at its centre; it is what expansion looks like from any point inside it. Hubble himself stayed publicly non-committal about the cosmological conclusion for the rest of his life, and campaigned unsuccessfully to have astronomy made eligible for a Nobel Prize.

Major achievements

• Proved in 1923 that the spiral nebulae are galaxies outside the Milky Way
• Used Cepheid variables as standard candles to measure intergalactic distances
• Established with Humason that recession speed is proportional to distance
• Created the classification of galaxies by shape still used today
• Expanded the known universe from one galaxy to countless ones

Life in brief

• 1889 — Born in Missouri: Later a heavyweight boxer and a Rhodes Scholar.
• 1913 — Reads law at Oxford: To please his father; returns to astronomy afterwards.
• 1919 — Joins Mount Wilson: And the 100-inch, then the largest telescope in the world.
• 1923 — A Cepheid in Andromeda: The nebula is another galaxy, far outside the Milky Way.
• 1929 — Speed against distance: With Humason's spectra: the points fall on a straight line.
• 1936 — The Realm of the Nebulae: His galaxy classification set out in full.
• 1953 — Dies in San Marino: Still non-committal about the expanding universe.

Explore the life of Hubble — five chapters

1. The Invented Life — A boxer, a Rhodes Scholar, and an accent
2. How Big Is the Universe? — The Great Debate, and a genuinely open question
3. The Mule Driver Who Took the Spectra — Milton Humason, and the hardest observing there was
4. A Universe Younger Than the Earth — The distance scale was badly wrong
5. Non-Committal to the End — The observation, and a refusal to say what it means

Read the five-chapter life of Edwin Hubble →

Where Hubble appears in your course

Edwin Hubble has a genuine claim on 3 lessons of the Pearson Edexcel International GCSE science course built into Incandio:

• The Hertzsprung–Russell Diagram — Physics: Absolute magnitude requires knowing how far away a star is, and that is the hardest measurement in astronomy. Hubble's 1923 breakthrough used Cepheid variable stars, which announce their true brightness through the period of their pulsation — a relationship discovered by Henrietta Swan Leavitt. Compare that true brightness with how faint the star looks and the distance follows. He used it to show that the Andromeda nebula lies far outside our own galaxy, which multiplied the size of the known universe at a stroke. He is the right person to ask how a distance can be measured without going anywhere.
• The Big Bang and its Evidence — Physics: The red-shift evidence on this page is Hubble's, and what makes him interesting here is his refusal to draw the conclusion everyone else drew from it. He plotted recession speed against distance, found the straight line the theory rests on, and then remained publicly non-committal about the expanding universe for the rest of his life, preferring to present the observation and leave the cosmology to others. He is the right person to ask about the difference between what a measurement shows and what a theory claims, and about how much caution is appropriate when your own data implies something extraordinary.
• Red-Shift — Physics: Statement 8.17 is Hubble's 1929 result and the whole of statement 8.18 rests on it. The individual red-shifts had largely been measured before, by Vesto Slipher, and most of the spectra Hubble used were taken by Milton Humason, who had arrived at Mount Wilson as a mule driver. Hubble's contribution was to pair each red-shift with a DISTANCE, using Cepheid variables, and to plot one against the other — at which point the points fell on a line. He is worth asking here about the plot itself: what it took to trust a straight line drawn through very few points with distances he knew were rough.

Begin

• Start a conversation with Hubble — a dramatised, historically grounded AI portrayal
• Read the Historical Brief
• Explore the life of Hubble — five chapters
• Find your exam topics · Meet all 208 figures