"Observation: You couldn't see a thing. Conclusion: Dinosaurs."The second planet from the sun, and the closest planetary orbit to the Earth's. As seen from the Earth, it's often the brightest point of light in the night sky — in fact, if you know where to look, it can sometimes be seen even in full daylight. This brightness is partly due to how close it gets to the Earth, and partly due to its bright whitish cloud cover. Interestingly, Venus appears brightest when it's in its crescent phase, because it's much closer to the Earth at that point that it is when it's in its gibbous phase. (Venus can't be seen when it's full, of course, since the sun is smack-dab between the Earth and the planet at that point.) Since Venus is never more than 40-some-odd degrees away from the Sun, it's most prominent right after sunset or right before sunrise, giving it the names "evening star" and "morning star." Venus used to be called "Earth's twin". It's 95% as big around as the Earth, it's got 90% of Earth's surface gravity, it's got an atmosphere with clouds in it, it's about the same distance from the sun — what could be so different? Well, for one, its surface temperature turned out to be nearly 900 degrees Fahrenheit, hotter than a self-cleaning oven and able to melt lead. The "air" consists almost entirely of carbon dioxide, and at the surface the pressure is equal to being half a mile under the ocean on Earth. And those clouds? They're not made of water vapor, they're made of sulfuric acid. What was once thought of as "Earth's Twin" turned out to be Earth's Evil Twin and a Bitch in Sheep's Clothing. These rather depressing details were revealed by the Soviet Venera space probes, sent to the planet in the late 1960s. Before that time, many Science Fiction authors held out hope that Venus might harbor life. Such hope was flimsy at best even before the Venera space probes, though; as early as the 1890s, spectrographs of the Cytherean atmosphere showed it to be made almost entirely of carbon dioxide, with no water vapor at all (meaning the clouds could not have been water clouds like those on Earth). Although the the top of the cloud layer was relatively cool, in 1962 the Mariner 2 probe revealed that the surface was several hundred degrees Fahrenheit. Its surface features, long hidden under the constant cloud cover, were finally mapped by the Magellan space probe using radar in the 1990s. The highest mountain is Maxwell Montes, almost 7 miles above the average surface level. If you stood on its peak, it'd be a downright chilly 380įC / 716įF, and a mere 60 atmospheres of pressure. The culprit for all this heat is the greenhouse effect — Earth's atmosphere is less than 1% carbon dioxide, while Venus's is over 90% carbon dioxide. Earth started with the same amount, but it ended up trapped in carbonate rock. Venus also started with the same amount of water as the Earth had, but it remained in vapor form (300 atmospheres worth) and created a super greenhouse effect with temperatures in the thousands of degreesnote . Eventually the water molecules dissociated into hydrogen and oxygen and escaped into space, leaving Venus high and dry. Due to Venus being mythologically associated with femininity, by convention all geographic features there are named after women or female entities, except for Maxwell Montes and Alpha and Beta Regio.note There is some argument over whether the proper adjective is 'Venusian', 'Venerean', or 'Cytherean' — just don't use 'Venereal'. At some point in the planet's early history, some big huge honkin' planetesimal struck it at an oblique angle, causing it to rotate very slowly backwards when compared with all the other planets in the Solar system. As a result of this super-slow rotation, a Cytherean solar day is nearly as long as a Venusian year. Not that you'd be able to see much difference between day and night while on the surface. The super-thick atmosphere bends light so severely that the horizon appears to curve upward, allowing you to see all the way around the planet. Twice. Whether you're on the day side or the night side, you'll see a hazy overcast sky that's about the same brightness everywhere — assuming you survive the lack of oxygen, the crushing pressures, and the hellish temperatures, that is. Well, now some optimistic stuff about Venus. There is a layer in its atmosphere where both temperature and pressure are Earthlike, located some 60 kilometers above the surface. The only non-Earthlike thing in this habitability zone is atmospheric chemistry, which is mostly CO2 with some sulfuric acid vapors; but it also means that normal Earth air will work in this atmosphere like a lifting gas, easily supporting a Cloud City. And as we all know from pop-psychology, women are from there.
— Carl Sagan, describing what Venus's cloud cover did for fiction
Venus in media