Forest Ray Moulton, an American astronomer known for a dominant early theory on how planets form, was born on this day in 1872. Moulton and Thomas Chrowder Chamberlin proposed in 1904 that the solar system formed after gas flares were ripped from the sun by the gravitational field of a passing star. The flares then condensed into "planetesimals" arrayed in a spiral extending from the sun; these planetesimals, the duo suggested, gradually accumulated material and became the planets we know today. Although it is now believed that gas ejected from the sun will not condense into solids, Moulton and Chamberlin's idea of a spiral galaxy influenced later astronomical observations, such as those of the rotating Andromeda galaxy.
[Source: Emily McMurray, Ed., Notable Twentieth Century Scientists (Gale Research Inc., ITP, 1995).]