The eastern & western elongations of Venus,2007-'17 II. The nocturnal hemisphere

摘要

Results for the planet's dayside were described in Part I. Here we discuss the nocturnal hemisphere, with details of infrared thermal emission (IRTE) imaging and the Ashen Light (AL). Images of the IRTE revealed up to nine topographic features upon the surface of the planet and enabled the slow rotation rate of the surface to be measured for the first time from amateur images. D. Gasparri recorded subtle, IR-absorbing low-altitude clouds of large scale, which were more prominent in 2009 than in 2017. The 2017 inferior conjunction saw remarkable high resolution reached by P. Miles and A.Wesley: the small bright spots they resolved upon the planet's surface might provide evidence for active volcanism.The AL was recorded in a small number of visual observations, with only a few sightings confirmed by a second observer. However, on 2009 Mar 12 the AL was imaged in the visible waveband by Gasparri and - at the same hour - independently observed at the eyepiece by G.Adamoli.The few positive AL sightings seem to be linked to solar Coronal Mass Ejection events. We review possible mechanisms to account for the AL.