[/caption]
The axial tilt of Venus is 177.3°. That’s a bit of a confusing number, so let’s figure out what’s going on here. Compare this number to the Earth’s axial tilt of 23.5°. Our tilt gives us such different seasons between summer and winter, so you’d expect that Venus’ much larger tilt would cause more extreme seasons.
Nope. But if you remember your high school geometry, you’ll realize what’s going on. A full circle is 360°. Half a circle is 180°. So if you subtract 177.3° from 180°, you get 2.7°. In other words, Venus is actually only tilted away from the plane of the ecliptic by only 2.7°. Venus is actually completely upside down – almost perfectly upside down.
In fact, Venus is the only planet in the Solar System that rotates backwards compared to the other planets. Seen from above, all the planets are turning in a counter clockwise direction. That’s why Asia sees the Sun first, then Europe, and then the Americas. Mars is the same, and so is Mercury, but Venus is rotating clockwise.
It’s possible that Venus was knocked upside down by a massive impact early in its history. it’s also possible that Venus just slowed down through tidal locking with the Sun, and was somehow spun slowly backwards through its interactions with the other planets.
Here on Earth, the axial tilt is responsible for the seasons. When it’s winter in the northern hemisphere, the north pole is tilted away from the Sun, and less of the Sun’s radiation falls on every square meter of ground. The opposite is true in the summer. Without a significant axial tilt, Venus doesn’t experience seasons like this. The temperature of Venus is a nice even 462°C everywhere on the whole planet.
We have written many articles about Venus for Universe Today. Here’s an article about Venus’ wet, volcanic past, and here’s an article about how Venus might have had continents and oceans in the ancient past.
Want more information on Venus? Here’s a link to Hubblesite’s News Releases about Venus, and here’s NASA’s Solar System Exploration Guide to Venus.
We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.