Simon Newcomb, American astronomer, moved to the United States from Canada in 1853 when he was about 18 years old. After teaching school in Maryland for some time he became a human computer in the Nautical Almanac Office of the United States Navy, and from January 1857 held a similar position at Harvard University. Meanwhile he studied at the university's Lawrence Scientific School, obtaining the degree Bachelor of Science (BS) in 1858. In his first scientific publication, in 1860, he argued that, as the orbits of asteroids do not intersect, they did not originate from the disruption of a larger planet. In September 1861 he was promoted to professor of mathematics in the US Navy, and assigned to the US Naval Observatory and Nautical Almanac Office in Washington, where he remained for the rest of his career. In 1868 he began his celebrated studies of the motion of the moon, a subject to which he contributed throughout his life. From 1871 to 1874 he was seconded to the United States Transit of Venus Commission, serving as its secretary. The commission organised eight American expeditions to observe the transit of 1874.
The United States Congress again appropriated funds to fit out eight expeditions to observe the next transit, on 6 December 1882. Newcomb came to the Cape of Good Hope as the leader of one of these expeditions, even though he had reservations about the accuracy of the planned observations for determining the solar parallax (and thus the earth-sun distance and the scale of the solar system). The other astronomers in his party were Lieutenant Thomas L. Casey, jnr, of the US Army, Ensign J.H.L. Holcombe, of the US Navy, and Mr Julius Ulke. Newcomb deciced to erect his instruments in the grounds of the Huguenot Seminary (later Huguenot College) in Wellington, Western Cape, where he obtained the participation in the observations of Miss A.P. Ferguson* and some members of her staff. The phenomenon was also observed independently by D. Gill* at the Royal Observatory in Cape Town, W.H. Finlay* at Aberdeen, A. Marth* at Touws River, and E.N. Nevill* at Durban.
The expedition's main telescope was a clock-driven photographic sun-telescope with a focal length of just over 12 m. A transit instrument was used to accurately determine the north-south line for the main telescope, while a 127 mm equatorial refractor was used to accurately time the "contacts" between Venus and the edge of the sun's disc. Observers were trained for the latter task with an artificial transit apparatus. Only the early part of the transit was visible from South Africa, as it ended after local sunset. The weather on 6 December was perfect and the observations were successful. However, the combined results of observations made all over the world contributed relatively little to a more accurate value of the solar parallax.
Newcomb became superintendent of the American Ephemeris and Nautical Almanac in September 1877 and served in this position until his retirement in 1897. During this time he conducted a critical review of all the fundamental data involved in the computation of the Ephemeris, namely fundamental star places, the mass and distance of the sun, motion of the moon, and orbits and masses of the planets and their satelites. All these were redetermined and new tables computed, a task that was largely completed during his lifetime. A number of classic memoirs resulted from this work, for example, he conducted fundamental investigations and produced accurate tables of the orbits of Neptune and Uranus, published in the Smithsonian Contributions to Knowledge in 1866 and 1873. In "A method of developing the perturbative function of planetary motion" (American Journal of Mathematics, 1880), he developed an improved method of deriving the periodic expressions needed to compute planetary perturbations. A more extensive publication on this topic followed in 1884. Another important work, Elements of the four inner planets and the fundamental constants of astronomy (1895), dealt with the orbits of the four inner planets. From 1884 to 1894 he served also as professor of mathematics and astronomy at Johns Hopkins University, Baltimore. His publications included many books for students and the general public, most of which were re-published in revised editions. These included Popular astronomy (1877), Astronomy for schools and colleges (1881), Elements of plane and spherical trigonometry (1882), Astronomy (1883), Elements of analytical geometry (1884), Principles of political economy (1885), Elements of the differential and integral calculus (1887), The stars: A study of the universe (1901), Astronomy for everybody (1902), and Spherical astronomy (1906). His numerous papers dealt mainly with the motions of the moon, planets and asteroids, positional astronomy, the astronomical constants, astronomical methods, probability theory, and general science.
Newcomb received many medals, prizes and awards, as well as honorary degrees from many universities. He was at various times president of the American Association for the Advancement of Science, the American Mathematical Society, the Philosophical Society of Washington, and the Astromomical and Astrophysical Society of America, and was elected a Fellow of the Royal Society of London in 1877. From 1874 he was the editor of the American Journal of Mathematics. As the greatest American astronomer of the 19th century a crater on the moon was named after him.