In many ways, Venus is a twin to our own Earth. It has a similar size, mass, density and chemical composition. Of course, its high temperatures and extreme atmospheric pressure make it different. And there’s another aspect of Venus that’s different from Earth; the rotation of Venus is longer than its year – oh, and Venus rotates backwards.
Remember from science class that a rotation is when an object spins once on its axis, and a revolution is when it travels once around in orbit around another object. So, the Earth takes one day to rotate on its axis, and it takes one year to revolve around the Sun in orbit. Venus, on the other hand, takes 243 days to turn once on its axis, and it takes almost 225 days to travel once around the Sun in orbit. As you can see, a day on Venus is longer than its year.
If that’s not strange enough, the rotation of Venus is backwards. Seen from above, all of the planets in the Solar System rotate counter-clockwise. This means that eastern regions see the Sun before western regions. But that rotation on Venus is backwards, so it’s going clockwise.
If you could stand on the surface of Venus. You would see the Sun rise in the west and then take 116.75 days to travel across the sky and then set in the east.
So why is the rotation of Venus backwards? Astronomers think that Venus was impacted by another large planet early in its history, billions of years ago. The combined momentum between the two objects averaged out to the current rotational speed and direction.
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.
We have recorded a whole episode of Astronomy Cast that’s only about planet Venus. Listen to it here, Episode 50: Venus.