Refraction and scattering in the atmosphere of the planet Venus: The Lomonossov arc

TL;DR

This paper reviews historical and modern observations of Venus transits, focusing on atmospheric refraction and scattering effects, and discusses the origin of the Lomonossov arc with implications for understanding Venus's atmosphere.

Contribution

It provides a comprehensive analysis of the atmospheric effects during Venus transits, linking historical observations to modern data and clarifying the nature of the Lomonossov arc.

Findings

Refraction and scattering significantly influence observed phenomena during Venus transits.

The Lomonossov arc is primarily caused by atmospheric refraction effects.

Modern observations help elucidate the atmospheric conditions of Venus.

Abstract

The main observations of 1761 by M. Lomonossov and those that followed are recalled by extending the discussion to other remarkable visual observations of the passages, then with more and more powerful imagers producing images in profusion. The modern treatment of parasitic effects is briefly recalled by focusing on the expert observation of 1761 which has recently been widely commented on and criticized. It included a spurious effect called the "black drop effect". The shell or aureole or atmospheric ring of Venus observed outside the solar disk is considered with reference to the today parameters of the Venus atmosphere. The contacts during the transit are discussed taking into account effects of scattering, absorption and the dominant effects of the refraction at the small angular distances found to be comparable to a fraction of the angular dimension of the planet. Modern observations of the 2004 and the 2012 transit are tentatively discussed to elucidate what is the arc of Lomonossov?