Arthur Eddington
Who Told Them To Find A Hotter Place · Astrophysicist · 1882–1944
Who worked out what holds a star up against its own weight, proposed in 1920 that stars run on hydrogen turning into helium, and told the critics who said the Sun was not hot enough for it to go and find a hotter place.
Who was Eddington?
Arthur Stanley Eddington was born at Kendal in 1882 into a Quaker family, and became Plumian Professor of Astronomy at Cambridge and director of its observatory. His central work is the theory of the interior of a star: a sphere of gas held up against its own gravity by the pressure inside it, with the pressure of the radiation itself doing a large share of the holding — from which he derived the relation between a star's mass and its brightness. The question the theory could not answer was where the heat comes from. Gravitational contraction gives the Sun a few tens of millions of years, and the geologists required thousands of millions, so the source had to be subatomic. In an address at Cardiff in 1920 he said what it must be: four hydrogen nuclei weigh appreciably more than one helium nucleus, so if the Sun is converting hydrogen into helium, the missing mass is available as energy by Einstein's relation, and the supply is ample. His critics objected that the Sun was not hot enough for the nuclei to come together, and he told them to go and find a hotter place. He was right, and the actual reaction chains were worked out by Bethe and von Weizsäcker in 1938 and 1939. In 1919 he organised and joined the eclipse expedition to Príncipe that measured the bending of starlight by the Sun — the first test general relativity passed — and he explained relativity to the English-speaking world better than anyone. His one great and lasting error was his public ridicule of Chandrasekhar's 1935 result that a sufficiently massive star cannot support itself at all, a conclusion he refused to the end.
Major achievements
- Built the theory of stellar interiors, with radiation pressure holding a star open
- Derived the mass–luminosity relation for stars
- Proposed in 1920 that stellar energy comes from hydrogen fusing into helium
- Organised the 1919 Príncipe eclipse expedition that confirmed the bending of starlight
- Explained general relativity to the English-speaking world in prose of great clarity
Life in brief
- 1882 — Born at Kendal: A Quaker family; his father dies when he is two.
- 1913 — Plumian Professor at Cambridge: And director of the observatory.
- 1919 — The Príncipe eclipse: Starlight bent by the Sun; relativity confirmed.
- 1920 — The Cardiff address: Hydrogen into helium as the source of a star's heat.
- 1926 — The Internal Constitution of the Stars: The mass–luminosity relation and the theory behind it.
- 1935 — The attack on Chandrasekhar: In public, at the Royal Astronomical Society; his lasting mistake.
- 1944 — Dies at Cambridge: Five years after Bethe supplied the cycles.
Explore the life of Eddington — five chapters
- A Quaker in a War — Conscientious objection, and an expedition as an alternative
- Príncipe — 29 May 1919, and a great deal of cloud
- What Holds a Star Up — Radiation pressure and the mass-luminosity relation
- Go and Find a Hotter Place — Cardiff, 1920, and the energy source of every star
- Chandrasekhar — January 1935, and a public humiliation
Read the five-chapter life of Arthur Eddington →
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