LOMONOSOV, THE DISCOVERY OF VENUS'S ATMOSPHERE, AND EIGHTEENTH CENTURY TRANSITS OF VENUS

Abstract

The discovery of Venus's atmosphere has been widely attributed to the Russian academician M.V. Lomonosov from his observations of the 1761 transit of Venus from St. Petersburg. Other observers at the time also made observations that have been ascribed to the effects of the atmosphere of Venus. Though Venus does have an atmosphere one hundred times denser than the Earth's and refracts sunlight so as to produce an 'aureole' around the planet's disk when it is ingressing and egressing the solar limb, many eighteenth century observers also upheld the doctrine of cosmic pluralism: believing that the planets were inhabited, they had a preconceived bias for believing that the other planets must have atmospheres. A careful re-examination of several of the most important accounts of eighteenth century observers and comparisons with the observations of the nineteenth century and 2004 transits shows that Lomonosov inferred the existence of Venus's atmosphere from observations related to the 'black drop', which has nothing to do with the atmosphere of Venus. Several observers of the eighteenth-century transits, includ- ing Chappe d'Auteroche, Bergman, and Wargentin in 1761 and Wales, Dymond, and Rittenhouse in 1769, may have made bona fide observations of the aureole produced by the atmosphere of Venus. Therefore, it appears that several observers—but not Lomonosov—should receive credit for first detecting the aureole due to refraction of sunlight by the atmosphere of Venus during a transit. This crucial observation occurred almost three decades before Johann Schroeter independently demonstrated the existence of the atmosphere of Venus from his analysis of extensions of the semicircle of light of the planet near inferior conjunction, which are produced by back-scattering of light by aerosol-sized particles.