The fascinating story of Franz von Paula Gruithuisen, a German astronomer who became prominent early in the nineteenth century, has inspired sci-fi writers to ponder exploring distant worlds like Mars and Venus. His attempts at explaining the wonders of space were filled with promise of mystery and awe. He was a fairly good observer who concentrated on the moon and the planets, but his imagination was, somewhat vivid. For instance, he discovered what he believed to be an artificial structure on the moon and described it as a collection of dark, gigantic artistic ramparts.
Gruithuisen's Moon Men
He speculated that Moon Men had built the structures on the surface of the moon. But it was in observing Venus that Franz von Paula Gruithuisen really outdid himself. He put forward a theory to explain the so-called ashen light that caused his more sober contemporaries to raise their eyebrows.
Look at our crescent moon and you can often see the unlighted side faintly shining. There is no mystery about this. The glow is caused by light reflected from Earth to the moon — as Leonardo da Vinci recognized long ago. But through the telescope, the same sort of radiance has been seen on Venus, where it is known as the ashen light. On Venus, it is not so easy to explain. Venus has no moon, and the earth could not illuminate it perceptibly. The lights of Venus have been mistaken for UFO's since the origin of science fiction literature.
Gruithuisen thought he had found an explanation. He noted that the light had been observed in 1759 and again in 1806, after an interval of 47 terrestrial and 76 Venusian years. He concluded:
"If we estimate that the ordinary life of an inhabitant of the planet lasts 130 Venus years, which amounts to 80 Earth years, the reign of an emperor of Venus might well last for 76 Venus years. The observed appearance is evidently the result of a general festival illumination in honour of the ascension of a new emperor to the throne of the planet."
Later Gruithuisen had second thoughts. He wondered whether the light might be due to the burning of large stretches of jungle to produce new farmland.
"large migrations of people would be prevented, so that possible wars would be avoided by abolishing the reason for them. Thus the race would be kept united."
There are objections to both of Gruithuisen's theories, and the ashen light itself remained controversial. Some astronomers dismissed it as a mere effect of contrast. Though it is always elusive, to see it properly one has to specialty fit the telescope eyepiece to hide the bright crescent of the planet. And, of course, one can never see Venus well. It needs to be seen against a really black sky for clarity, because it is always too low over the horizon.
Seas, Auroras, and Lightning Flashes on Venus
Among possible explanations for the ashen light, astronomers have suggested fluorescence in the planet's seas, auroras, and lightning flashes. It looks as if the lightning theory was more likely.
A fleet of spacecrafts approached Venus from as far back as the Pioneer multiprobe from the United States. Russian Veneras made controlled landings, though without sending back pictures, as their predecessors had done. Over the years many images have made their way into the digital ethos. Many strange surface features cover the planet.
The Tesserae of Venus
Most notable, a huge rift valley 5 kilometers deep, 280 kilometers wide, and stretching at least 1,440 kilometers, apparently with no sudden beginning or end. This remarkable valley dwarfs even the Valles Marineris on Mars and makes our own Grand Canyon seem like a mere mud crack. The Tesserae of Venus are one of the marvels of the universe.
Just as interesting was the revelation that there is continuous lightning up to 32 kilometers above ground level. Both the Venera and the Pioneer orbiters originally detected as many as 25 discharges per second. An observer on Venus would see what appeared to be a continuous, eerie glow and would hear ceaseless thunder
There was also a second glow discovered that was thought to be caused by chemical reactions in the superheated atmosphere close to the planet's surface. This glow seems to start about 16 kilometers above ground level, and combines with the lightning to make up the ashen light, an effect that has been seen by nearly all serious Venus Watchers.
Future Cloud Cities of Venus
Astronomers of the mid 20th century, still thought that Venus was covered by oceans, with a surface temperature we would find quite tolerable. But by the the 1980s, scientists were resigned to finding a carbon dioxide atmosphere about 90 times as dense as our own, clouds containing sulfuric acid, and a surface temperature above 450°C.
The new findings made Venus an even more peculiar world than we had expected since man began gazing at the stars. Any future traveler who might step outside his spaceship to admire the view would be simultaneously poisoned, squashed, fried, and corroded. It now seems that he might also be deafened. The thunderclaps on Venus must be vastly louder than anything we hear on Earth. Over the years, many people have suggested that we seed the atmosphere of Venus with bacteria to break up the carbon dioxide molecules and release free oxygen in order to prepare the planet for colonization. It now seems unlikely that such plans will ever be practical. In many ways, then, Venus has been a disappointment. Yet it remains one of the most fascinating bodies in our Solar system.