Venus takes 243 Earth days to spin once on its axis. It takes 225 Earth days to complete one full orbit around the Sun.
Read those two numbers again. The rotation is slower than the orbit. Venus finishes an entire trip around the Sun before it finishes turning around once. A year on Venus is shorter than a day.
And it gets stranger. Venus is the only planet in the solar system that spins backwards — what astronomers call retrograde rotation. Every other planet rotates west to east, like Earth. Venus rotates east to west. If you could stand on the surface, the Sun would rise in the west and set in the east.
This backward spin creates another paradox. Because Venus is slowly rotating one way while orbiting the other, the Sun appears to move across the sky faster than the planet actually turns. The result: a sunrise-to-sunrise solar day — the day you would actually live through — lasts about 117 Earth days, not 243. The Sun rises roughly twice per Venusian year, even though the planet has not yet finished a single full rotation.
For comparison, here is how long a day lasts on each planet:
- Jupiter: ~10 hours (fastest spinner)
- Earth: 24 hours
- Mars: 24 hours 37 minutes
- Mercury: 59 Earth days (rotation)
- Venus: 243 Earth days (rotation) — the slowest in the solar system
Nobody knows for certain why Venus spins so slowly, or backwards. The leading theory is that a massive collision early in the planet's history — a planetesimal impact — reversed its rotation entirely. But this has never been confirmed.
What is confirmed is the surface waiting below those spinning clouds: 465°C (869°F), hotter than Mercury despite being further from the Sun. Atmospheric pressure 90 times Earth's — the equivalent of being 900 metres (3,000 ft) deep in the ocean. It rains sulfuric acid, though the drops evaporate before they reach the ground. Venus is nearly identical in size to Earth — our closest neighbour, our "twin" — and completely, spectacularly uninhabitable.
A planet that takes longer to turn around once than to travel 680 million km (422 million mi) around the Sun, where the Sun rises in the wrong direction, it rains acid, and the air would crush you flat. Somewhere in the universe, there is a word for this. In English, we just named it after the goddess of love.