19th-Century Achievements

Abstract

In the study of long-period effects old observations have a long-lasting value as they help to extend the time interval over which the effect can be traced. Most visual binaries have not completed a revolution since discovery, and therefore, have not been reobserved in the same section of the orbit. To the present-day orbit investigator, 150 yr old measurements still have far more interest than a mere historical, and so the yellowed folio pages of the ‘Mensurae micrometricae’ by F. G. W. (Wilhelm) Struve, 1837, are still consulted. For the first time, the visual double stars appear here as an independent, systematically executed program of discovery and reobservation. The measurements with the new micrometer installed in 1821 at the 9 in. Fraunhofer refractor have an accuracy which is really outstanding for those days, and good even by present standards; they are also free from marked systematic errors. The arrangement of the observations became standard practice. W. Struve also introduced counting the position angles from 0° through 360°, instead of recording quarants which had been the previous custom, and had caused frequent mistakes. He later decided to impose a separation limit on the double stars, namely 32" for brighter and 16" for fainter stars. Of the 3134 stars with the key letter 2— almost all of which had been published in the 1827 ‘Catalogue novus stellarum duplicium’ —almost 500 entries were thus rejected, mostly wide pairs outside the limits. The comprehensive voulume ‘Stellarum duplicum et multicium mensurae micrometricae’ was followed 1852 by the ‘Positioners mediae’ which contained the meridian results.