Periods Between 100 and 1000 Years

Between periods of 100 and 1000 years lie many of the binaries that can be seen with small telescopes such as Castor (445 years), y Leo (618 years) and y Vir (169 years). The Sixth Catalogue of Orbits of Visual Binary Stars, from the United States Naval Observatory (on the CD-ROM) attempts to list and assess the various orbits which have been calculated for visual binaries. Each orbit is graded from 1 (definitive) to 5 (preliminary) and there are no definitive orbits for binaries with periods greater than that of 70 Oph (88.38 years). (The Sixth Catalogue is the regularly updated version available on-line at the USNO website.) This is due to the fact that it is only from around 1830, when F.G.W. Struve was well into his stride at Dorpat working with the 9.6-inch refractor, that reliable (and numerous) measures exist. Clearly it is still important to work on these systems, even though the results may not be used for several centuries. It was the great Danish astronomer Ejnar Hertzsprung who said "If we look back a century or more and ask 'What do we appreciate mostly of the observations made then?' the general answer will be observations bound to time. They can, if missed, never be recovered. Of these observations, measures of double star contribute a major part."

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