Edwin Hubble

In 1923-24 Hubble used the 100-inch telescope at Mount Wilson to find Cepheid variable stars in the Andromeda nebula, and soon in M33 and NGC 6822. Their periods and brightness put Andromeda at roughly 900,000 light-years in his 1929 paper, far outside the Milky Way, and effectively settled the long dispute over whether spiral nebulae were separate galaxies. Later work showed his distance scale was too small; Andromeda proved about twice as far.

In 1929 Hubble set his galaxy distances against measured redshifts, mostly Vesto Slipher's, and reported that more distant galaxies appear to recede faster, at about 500 km/s per megaparsec. With Milton Humason, who measured fainter galaxies, he extended the relation from 1931. It became the observational basis of the expanding-universe picture, though Hubble wrote of 'apparent' velocities and kept the interpretation open, and Georges Lemaitre had derived such a relation and estimated its rate in 1927, so historians still debate how to share the credit.

In 1926 Hubble proposed a classification of galaxies into ellipticals, spirals, barred spirals and irregulars. The 'tuning fork' diagram that summarises it appeared in his 1936 book The Realm of the Nebulae, and Allan Sandage completed the system after Hubble's death. The Hubble sequence is still the standard starting point for describing galaxy shapes.

In the 1920s Hubble's Mount Wilson colleague Adriaan van Maanen reported rotation measurements of spiral nebulae that, if the nebulae were distant, would have implied impossible speeds. According to the American Institute of Physics history, Hubble first took apart van Maanen's claim of corroboration in a private talk, then published his own remeasurement of four nebulae, which showed systematic errors in van Maanen's figures. Later van Maanen printed a short note saying his motions should be viewed 'with reserve', an arrangement the history says was negotiated with Hubble and the journal's editor.

This episode is consistent with a willingness to contradict a colleague's data openly, while settling the dispute by negotiating how the record would be presented rather than staging a direct confrontation. Conflict Tolerance

Hubble's 1926 galaxy-classification paper contains a footnote asserting priority over a similar scheme by Knut Lundmark; Allan Sandage says some of Hubble's complaints, which he rarely made public, were unfounded. In a letter to Willem de Sitter of 21 August 1930, quoted by the astronomer David Block, Hubble wrote that he considered the velocity-distance relation, 'its formulation, testing and confirmation, as a Mount Wilson contribution' and was 'deeply concerned in its recognition as such'.

These two episodes are consistent with a strong concern for priority and credit. Whether the omissions of earlier work in his 1929 paper were deliberate is disputed and is not part of this reading. Competitiveness

After three years at Oxford, Hubble passed the Kentucky bar examination in 1913 but, according to Osterbrock and colleagues, left no record of practising law; he taught Spanish and physics and coached basketball at a high school in New Albany, Indiana. In 1914 he wrote to his Chicago professor Forest Moulton about returning as a graduate student, and Yerkes Observatory offered him a service scholarship. He later said he had 'chucked the law for astronomy', knowing he might be second-rate or third-rate.

This pivot illustrates taking the initiative to change direction: the move to astronomy came from his own request, at some cost in the security of a profession he was already qualified for. Proactive Agency