Canadian-born US mathematician and astronomer who compiled charts and tables of astronomical data with phenomenal accuracy. His calculations of the motions of the bodies in the Solar System were in use as daily reference all over the world for more than 50 years, and the system of astronomical constants for which he was most responsible is still the standard.

Newcomb was born in Wallace, Nova Scotia, and had little or no formal education. In his teens he ran away to the USA, and eventually enrolled at Harvard. In 1861 he joined the navy, where he was assigned to the US Naval Observatory at Washington DC, and in 1877 put in charge of the American Nautical Almanac office. From 1884 he was also professor of mathematics and astronomy at Johns Hopkins University. He retired with the rank of rear admiral.
At the Nautical Almanac office, Newcomb started the great work that was to occupy the rest of his life: the calculation of the motions of the bodies in the Solar System. The results were published in Astronomical Papers Prepared for the Use of the American Ephemeris and Nautical Almanac, a series that he founded 1879.
With his British counterpart Arthur Matthew Weld Downing (1850-1917), Newcomb established a universal standard system of astronomical constants. This was adopted at an international conference 1896, and again 1950.