Venus with unusual facts

 Reality of Venus with some interesting facts 

Almost all planets in the Solar System spin anti-clockwise on their axis and orbit the Sun in an anti-clockwise direction. Venus also orbits the Sun anti-clockwise but spins clockwise on its axis. One theory for this unusual  rotation is that it was knocked off its upright position earlier in its history! The only other planet in the Solar System to spin clockwise is Uranus. Astronomers believe that at some point, a colliding celestial body tilted Venus so far off its original position that it is now upside down. The only other planet to spin in a weird direction is Uranus, which spins on its side, probably the result of another collision early on in its life. The clouds of sulphuric acid in Venus’ atmosphere make it reflective and shiny, obscuring our view of its surface. Its brightness makes it visible even during the day, if it’s clear and you know where to look.

A Venusian day is about 243 Earth days, while a Venusian year lasts about 225, and because the planet rotates backwards compared with Earth and most other planets, the Sun would rise in the west and set in the east. Venus takes about 243 Earth days to turn once on its axis. It takes about 225 Earth days to circle the Sun. On those figures a single rotation outlasts a whole Venusian year, which is the basis for the popular line that a day on Venus is longer than a year. Venus is hotter than Mercury, despite being further away from the Sun. Its mean temperature is 462°C. This is because of the high concentration of CO2 in Venus’ atmosphere, which works to produce an intense greenhouse effect. Heat is trapped in the atmosphere like a blanket, causing the temperature of the planet to be much higher than its proximity to the Sun would suggest.

“Day” can mean two things, and on Venus they are nowhere near each other. The first is the rotation period, the time the planet takes to spin once relative to the distant stars. Astronomers call this the sidereal day. On Venus it runs to about 243 Earth days, and according to NASA’s Venus fact sheet that is indeed longer than the planet’s 225-day orbit. The second is the solar day, the time from one sunrise to the next. That is the day you would actually live through, and on Venus it lasts about 117 Earth days. A little over half a Venusian year. The Sun comes up, sets and comes up again roughly twice in every trip around the Sun. NASA’s Space Place makes the consequence concrete: because the Sun rises only about every 117 Earth days, it rises close to twice during a single Venusian year, even though, by the rotation count, it is still the same long day.

Venus has 90 times the atmospheric pressure of Earth. That’s about the same as the pressure found at a depth of 1km in the Earth's oceans. It is thought that Venus was named after the beautiful Roman goddess (counterpart to the Greek Aphrodite) due to its bright, shining appearance in the sky. Of the five planets known to ancient astronomers, it would have been the brightest. Venus rotates backwards. Most planets in the Solar System, Earth included, spin in the same direction they orbit, west to east, which is why our Sun rises in the east. Venus turns the other way. Stand on its surface, somehow, and the Sun would come up in the west and go down in the east. That reverse spin is also what pulls the solar day so far below the sidereal day. As Venus moves around its orbit, its slow backward rotation brings the Sun back to the same point in the sky sooner than a forward spin would. Venus was the first planet to have its motions plotted across the sky, as early as the second millennium BC. Because Venus is easy to spot with the naked eye, it is impossible to say who discovered the planet. But over the centuries we have been able to measure Venus’ motions, including the rare transit of Venus, when the planet appears to cross in front of the Sun.

The thick atmosphere would change the experience further. Venus is wrapped in dense cloud, so any sunrise at the surface would be a slow brightening rather than a sharp event at the horizon. The surface itself, at about 465 degrees Celsius and under crushing pressure, is not somewhere you would linger to watch it. How Venus ended up with a slow backward spin is an open question, not a solved one. One line of thinking points to a large impact early in the planet’s history, the kind of collision which could knock a young planet’s rotation off course and even reverse it. Another points to the atmosphere: solar heating drives strong atmospheric tides in Venus’s dense air, and over a very long time these may have braked the spin and helped tip it into reverse. Both are hypotheses. Neither is confirmed, and there is no agreement on which mattered more, or whether both played a part. What is measured, rather than inferred, is the rotation rate itself. Earth-based radar observations have pinned Venus’s sidereal day at close to 243 Earth days, while also showing that the exact spin period can vary by tens of minutes, likely because the dense atmosphere exchanges angular momentum with the solid planet.

Following the rules of Latin, we should say ‘venerean’ as the adjective to describe things related to Venus. However, this is deemed to be too close to the word ‘venereal’. The more commonly used word is ‘Venusian’ despite its clunky etymology. Venus does take longer to spin once than to complete one orbit, and it is the only planet in the Solar System for which that is true. But the day you would live through there is shorter than the year, a little over half of it. Venus does not hold a single sunrise across more than a year. It turns slowly, and backwards, and so the Sun comes up twice between one Venusian New Year and the next.