Which is the only planet whose day is longer than its year?

The only planet in our Solar System whose day is longer than its year is Venus. This means that Venus takes more time to rotate once on its axis than it takes to complete one orbit around the Sun. A day on Venus lasts about 243 Earth days, while its year — the time it takes to travel around the Sun — is only 225 Earth days.

This unusual fact happens because Venus rotates very slowly and in the opposite direction compared to most other planets. This backward spin is called retrograde rotation, meaning that if you stood on Venus, the Sun would appear to rise in the west and set in the east, the reverse of what we experience on Earth.

Scientists believe that Venus’s slow rotation may be the result of a massive collision with another large object early in its formation, which could have changed both its rotation speed and direction.

Venus is often called Earth’s twin because it is similar in size, mass, and composition. However, its thick atmosphere of carbon dioxide (CO₂) traps heat through a strong greenhouse effect, making Venus the hottest planet in the Solar System, even hotter than Mercury. The surface temperature can reach around 465°C (869°F), which is hot enough to melt lead.

The study of Venus’s motion helps scientists understand how planetary rotations and orbits affect climate and atmospheric conditions. By comparing Venus with Earth, researchers can learn more about global warming, atmospheric pressure, and planet formation.

In simple terms, Venus shows us how unique each planet can be. Its extremely slow spin and reversed rotation make it the only planet where a single day lasts longer than its entire year, an extraordinary feature that fascinates astronomers and science learners alike.