THE planet Venus currently playing as the evening star, has been conspicious in the western sky of late, shining with a solitary brilliance that makes it easy to see where Henry Wadsworth Longfellow found his inspiration:
Just above yon sandy bar,
As the day grows fainter and dimmer,
Lonely and lovely, a single star
Lights the air in a dusky glimmer.
Just recently indeed, Venus has been at its dazzling best or magnitude -4.5 as astronomers soberly and paradoxically like to call it.
The perennial brightness of Venus is partly accounted for by the fact that it is completely enveloped in an unbroken layer of dull yellowish cloud. The cloud, rather unpleasantly, consists of tiny, droplets of concentrated sulphuric acid, but from our perspective it has the interesting effect of reflecting about 80 per cent of the incoming solar radiation. The planet's very high reflectivity is in contrast to the situation here on Earth, where cloud cover is on average about 50 per cent, and only some 30 per cent of the incoming sunlight is reflected.
The ancient Greeks had two names for Venus. When it appeared as the evening star, they called it Hesperus - meaning "western"; when they saw it as the morning star - which presumably they took to be a different heavenly body - they called it Lucifer. Lucifer, as it happens, is rather more appropriate.
The surface of Venus is a rocky plain, sweltering under a dull orange sky. Since the "air" is composed almost entirely of carbon dioxide, Venus is no stranger to the "greenhouse effect". Because it is closer to the sun, almost twice as much energy reaches the planet as reaches Earth, and a great deal - of this energy is trapped by the CO2. As a result, Venus has a surface temperature of nearly 460 degrees Celsius - hot enough to cause the rocks on "the "night" side of the planet to glow a dull deep red in the sultry darkness. This whole eerie landscape is swept by fierce winds which would make the Earth's most savage hurricanes seem like a gentle summer breeze.
The atmosphere of the planet is very dense, resulting in an atmospheric pressure of 90,000 hectopascals, compared to our average of 1013. In the unlikely event of any human being ever standing in the dim twilight on its scorching surface, he or she would be crushed by its heavy atmosphere of unbreathable gases, and simultaneously exposed to a slow persistent drizzle of sulphuric acid to borrow from a phrase from Jean Paul Sarte, l'Enfer, c'est Venus.