Spencer Jones, Harold (1890–1962)
Harold Spencer Jones was an English astronomer who became the tenth Astronomer Royal and led a decade-long worldwide effort to determine the distance to the Sun by triangulating the distance of the asteroid Eros when it passed near Earth in 1930–1931: he photographed Eros more than 1,200 times and reduced the data from other observers in one of the most impressive computational feats of the pre-computer era.
Educated at Cambridge, Spencer Jones was successively astronomical assistant at the Royal Observatory, Greenwich, His Majesty's Astronomer at the Cape of Good Hope, and, from 1933 to 1955, director of the Royal Observatory and Astronomer Royal. His work was devoted to fundamental positional astronomy. At the Cape he worked on proper motions and parallaxes. After his monumental effort in solar astrometry, he showed that small residuals in the apparent motions of the planets are due to the irregular rotation of Earth. After World War II he supervised the move of the Royal Observatory to Herstmonceux, where it was renamed the Royal Greenwich Observatory. (Some sources list his surname as Jones; he preferred Spencer Jones.)
Spencer Jones became a strong advocate of the view that extraterrestrial life is probably common in the Universe. In the first edition of his influential Life on Other Worlds,1 published in 1940, he echoed the conclusions of Jeans and others, based on the then popular catastrophic hypothesis that
... life is not widespread in the universe ... not more than a small proportion of the stars are likely to have planets at all. With the usual prodigality of Nature, the stars are scattered far and wide, but only the favored few have planets that are capable of supporting life.
However, by the second edition in 1952, with the rise of Weizsäcker's updated version of the nebular hypothesis, he was able to write
On this important problem of the origin of the solar system and of planetary systems in general, there has been a marked change in outlook in the past few years from that of twenty years ago. Astronomers then felt pretty confident that the solar system was something very exceptional; now it appears much more probable that the formation of a planetary system may occur as one of the normal courses of stellar evolution.
As to the likelihood of life evolving on the surface of a suitable planet, Spencer Jones was already optimistic in 1940:
[I]t seems reasonable to suppose that whenever in the Universe the proper conditions arise, life must inevitably come into existence. This is the view that is generally accepted by biologists.
1. Spencer Jones, Harold. Life on Other Worlds. N.Y.: New American Library (1951).