Beyond the planets: early nineteenth-century studies of double stars

Abstract

In 1837 the German-born astronomer F. G. W. Struve published his famous catalogue of double stars. For Struve this was the culmination of 12 years' detailed observation of a class of celestial objects lying exclusively beyond the solar system; for historians of astronomy it poses the problem of explaining why the study of double stars became a significant part of astronomical endeavour, as it did, during the 1820s and 1830s. For, although Struve's interest was extreme, it was shared to a lesser extent by several eminent contemporaries, including John Herschel, Friedrich Bessel, Johann Encke, James South and Félix Savary. Their combined efforts represented an important transition in astronomy: for the first time one of the emphases of the subject moved beyond the solar system to the so-called fixed stars. The question of the emergence of interest in double stars is of historical significance, therefore, as it is related to the problem of the origins of ‘stellar astronomy’. This essay is thus intended to offer an explanation of astronomers' interest in double stars, and to tackle the related question of whether this transition constituted a major break in the history of astronomy. Furthermore it is proposed that answers to these problems may be found by considering the practice of astronomy dominant during the first half of the nineteenth century. Astronomers in this period were overwhelmingly concerned with a refined form of positional astronomy. The problems they chose to solve were by and large related to the difficulties of the accurate reduction of observational data, and the compilation of reliable tables and star charts, which were then used as a background against which the motions of solar system objects were plotted. By assessing individuals' studies of double stars within this context it can be seen firstly that such studies were no more or less than specific examples of a general case, and secondly that the stars themselves were not usually of intrinsic interest. In general it was the positions of the stars on the