Harold Spencer Jones


English astronomer who made a determination of solar parallax, using observations of the asteroid Eros. He also studied the speed of rotation of the Earth, and the motions of the Sun, Moon, and planets.
Spencer Jones was born in London and studied at Cambridge. He worked at the Royal Observatory, Greenwich, 1913-23; was His Majesty's Astronomer on the Cape of Good Hope, South Africa, 1923-33; and ended his career as the tenth Astronomer Royal 1933-55.
While at the Cape of Good Hope, Spencer Jones published a catalogue containing the radial velocities of the southern stars, calculated the orbits of a number of spectroscopic binary stars, and made a spectroscopic determination of the constant of aberration. In 1925, he obtained and described a long series of spectra of a nova which had appeared in the constellation of Pictor.
Spencer Jones proved that fluctuations in the observed longitudes of the Sun, Moon, and planets are due not to any peculiarities in their motion, but to fluctuations in the angular velocity of rotation of the Earth. He also investigated the Earth's magnetism and oblateness, and he estimated the mass of the Moon.

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