Arthur Eddington

Sir Arthur Stanley Eddington (1882 – 1944)

Arthur Eddington was a British astronomer, physicist and mathematician. He was born in Cumbria, UK before moving to Weston-super-Mare as a child. He was not from a wealthy family but did so well at school that he got a scholarship to go to Owen’s College, Manchester. He graduated with a physics degree in 1902. Arthur was then offered a position at Trinity College, Cambridge where he completed his master’s degree. He worked at the Royal Observatory in Greenwich, London, before returning to Cambridge five years later.

He was the first person to propose that stars were powered by the nuclear fusion of hydrogen into helium. The limit to how bright a star can be before it begins to collapse is named after him, the Eddington Luminosity.

Einstein’s Theory of Relativity

He is most famous, for his work on Einstein’s Theory of Relativity. Arthur carried out observations of a solar eclipse to confirm the theory. This work was considered so important that it prevented him beginning military service during the First World War. Arthur was happy about this as he was a pacifist, but he did offer to join an ambulance unit, or work as a harvest labourer on home soil.

Arthur viewed the eclipse from the island of Principe, off the west coast of Africa. He chose that location because there was a good chance of clear skies, and he could view the eclipse in full there. During the darkness of the eclipse, Arthur took photographs of stars close to the Sun. These stars are normally blocked by the light of the Sun during the day. Arthur observed that stars close to the Sun had their light shifted by the Sun’s gravitational field. This confirmed Einstein’s Theory of Relativity.


Eddington was also heavily involved with the development of the first generation of general relativistic cosmological models. He had been investigating the instability of the Einstein universe when he learned of both Lemaître’s 1927 paper postulating an expanding or contracting universe and Hubble’s work on the recession of the spiral nebulae. He felt the cosmological constant must have played the crucial role in the universe’s evolution from an Einsteinian steady state to its current expanding state, and most of his cosmological investigations focused on the constant’s significance and characteristics. In The Mathematical Theory of Relativity, Eddington interpreted the cosmological constant to mean that the universe is “self-gauging”.

Eddington number for cycling

Eddington is credited with devising a measure of a cyclist’s long-distance riding achievements. The Eddington number in the context of cycling is defined as the maximum number E such that the cyclist has cycled E miles on E days.

For example, an Eddington number of 70 miles would imply that the cyclist has cycled at least 70 miles in a day on at least 70 occasions. Achieving a high Eddington number is difficult since moving from, say, 70 to 75 will (probably) require more than five new long distance rides, since any rides shorter than 75 miles will no longer be included in the reckoning. Eddington’s own life-time E-number was 84.

He later wrote this short poem about the discovery:

Oh leave the Wise our measures to collate

One thing at least is certain, LIGHT has WEIGHT,

One thing is certain, and the rest debate—

Light-rays, when near the Sun, DO NOT GO STRAIGHT.

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