If you were standing on the surface of Venus, the Sun would rise in the west. Honestly, that’s just the start of the weirdness. You’d be waiting a long time for breakfast, too. See, when people ask how long is Venus day, they usually expect a simple number like 24 hours. But Venus doesn't do "simple." Depending on how you define a day, the answer is either 117 Earth days or 243 Earth days.
It's a bit of a cosmic mess.
On Earth, our day and our rotation are basically the same thing. On Venus, the planet spins so slowly that it actually takes longer to complete one rotation than it does to orbit the Sun. You heard that right. A year on Venus is shorter than its "sidereal" day.
The Difference Between Two Different "Days"
To really get why the clock on Venus is so broken, you have to understand the two ways astronomers measure time.
First, there’s the sidereal day. This is how long it takes for a planet to spin 360 degrees on its axis relative to the stars. On Venus, this takes about 243.0226 Earth days. This is the slowest rotation of any planet in our solar system. For comparison, it’s like the planet is barely crawling.
Then you have the solar day. This is what you’d actually experience if you were standing on the ground—the time from one noon to the next. Because Venus is moving around the Sun while it's slowly spinning "backwards" (retrograde), the Sun actually returns to the same spot in the sky much faster than the planet completes a full spin.
A solar day on Venus is roughly 116.75 Earth days.
So, if you lived there, you’d see a sunrise every 117 days or so. You'd get about 58 days of blistering, soul-crushing sunlight followed by 58 days of pitch-black night. Not exactly a weekend getaway.
Why How Long Is Venus Day Is Always Changing
Here is the really wild part: the length of a day on Venus isn't even constant. It’s "wobbly."
Back in the 1990s, the Magellan spacecraft mapped the surface and clocked the rotation. But when the European Space Agency’s Venus Express arrived about 15 years later, they found the rotation had slowed down. The planet was "lagging" by about 6.5 minutes.
That might not sound like much, but for a whole planet to change its speed that quickly? That’s massive.
Recent studies, including some pretty groundbreaking work by Jean-Luc Margot at UCLA using radar speckle tracking between 2006 and 2020, have shown that the day length can fluctuate by as much as 20 minutes.
"Venus’s powerful atmosphere teaches us that it’s a much more integrated part of the planet that affects absolutely everything, even how fast the planet rotates." — Stephen Kane, UC Riverside Astrophysicist.
✨ Don't miss: The View of Antarctica From Space: What Most People Get Wrong
Basically, the atmosphere of Venus is so thick and heavy—90 times the pressure of Earth’s—that it actually drags on the surface. Imagine trying to spin a ball inside a vat of thick honey. The friction between the fast-moving winds (which circle the planet every four days!) and the rocky ground literally pushes and pulls on the planet's rotation.
Why Does It Spin Backwards?
Most planets in our neighborhood spin counter-clockwise. Venus is the rebel. It has what we call retrograde rotation.
There are two main theories for why this happened:
- The Big Smash: Early in the solar system's history, a massive object—maybe the size of a small planet—slammed into Venus and flipped its rotation or knocked it completely upside down.
- Atmospheric Tides: The Sun’s gravity pulls on that thick, soup-like atmosphere, creating "tides" that slowly put the brakes on the planet’s original rotation and eventually started it spinning the other way.
Honestly, it could be a mix of both. Science is still debating it.
Survival on a 117-Day Cycle
If you’re planning a trip (don't), the day-night cycle would be the least of your problems. The surface temperature is a constant 460°C (860°F). Because the atmosphere is so thick, the heat doesn't even escape during that long, 58-day night. It stays just as hot in the dark as it does in the light.
There’s no "cool evening breeze" on Venus. Just crushing pressure and heat that can melt lead.
Practical Takeaways for Space Enthusiasts
Knowing how long is Venus day is more than just a trivia fact. It’s a massive hurdle for future missions.
- Landing Accuracy: If the rotation changes by 20 minutes, a lander could miss its target by several kilometers. Engineers have to use real-time radar data to "aim" their spacecraft.
- Power Sources: Solar power is tricky. You have to survive nearly 60 Earth days of darkness, meaning batteries or nuclear power (RTGs) are the only way to stay alive.
- Super-Rotation: Because the atmosphere spins 60 times faster than the ground, any balloon or "cloud city" concept would be zipping around the planet every 4 days, even though the ground below is barely moving.
If you want to track Venus yourself, it’s currently one of the brightest objects in the sky. Look for it as the "Morning Star" or "Evening Star" depending on its position relative to the Sun. Just remember, while you’re watching it for a few minutes before bed, the folks on the surface (if there were any) would still be waiting months for the Sun to move a few inches across the sky.
✨ Don't miss: Finding the Right Names for Screen Names: Why Your Digital Identity Actually Matters
To keep up with the latest rotation data, you can check the NASA PDS (Planetary Data System) or follow the updates from the upcoming DAVINCI and VERITAS missions, which are specifically designed to solve these rotation mysteries once and for all.