The Ashen Light: An auroral phenomenon on Venus

We have collected and analyzed 129 visual observations of the Ashen Light, the luminous glow on the dark side of Venus, made between 1954 and 1962. Spectroscopic and photometric studies attempting to detect dark side emission on Venus are reviewed and discussed in light of the visual occurrence of the glow. We have found a general increase in the geomagnetic index coinciding with the occurrence of the Ashen Light at times of inferior conjunction of Venus, which suggests that the Ashen Light is an auroral phenomena due to solar particle bombardment on the dark side of Venus. This possibility is explored in terms of the nature and characteristics of the visual Ashen Light observations and in terms of the recent Mariner V and Venera-4 data on the upper atmosphere of Venus.