The definition of "day" that is important here is the "solar day". Venus has the longest day of all the planets. There’s more than one kind of day. Mercury has the longest solar day.

One day on Venus lasts the equivalent of 243 days and 26 minutes here on Earth. It orbits the Sun every 224.65 Earth days, so a day is nearly 20 Earth days longer than its year. The Earth is the only planet with an approximately 24-hour day. The planet Jupiter has the shortest day of all the eight major planets in the Solar System. A Day On Venus: Also known as “Earth’s Twin”, Venus is the second closest planet to our Sun – ranging from 107,477,000 km at perihelion to 108,939,000 km at aphelion. Just to be clear, this answer to ‘which planet has the longest day’ is based on this criteria: a planets day is how long it takes it to complete one rotation on its axis. On Earth, a sidereal day is almost exactly 23 hours and 56 minutes. The winter solstice has the shortest day and the longest night of the year. A day on Jupiter lasts only nine hours and 55 minutes. Venus has the longest day of any planet in our solar system.It completes one rotation every 243 Earth days.Its day lasts longer than its orbit. The Planet with the Longest Day: Venus; a day on Venus takes 243 Earth days. A day on Jupiter Venus has the longest period of rotation. Another way to measure a day is to count the amount of time it takes for a planet to completely spin around and make one full rotation. Another way to measure a day is to count the amount of time it takes for a planet to completely spin around and make one full rotation. It spins around on its axis once every 9 hr 55 min 29.69 sec.

The Planet with the Shortest Day: Jupiter. On Earth, a sidereal day is almost exactly 23 hours and 56 minutes.

The planet is Mercury. Venus has the longest period of rotation. Jupiter has a small axial tilt of only 3.13 degrees, meaning it has little seasonal variation during its 11.86-year-long orbit of the Sun. A day on Venus lasts 243 Earth days. An Earth day is 24 hours no matter what planet you are on. We know how long an Earth day is, but how about the other planets in our solar system? A Day On Venus: Also known as “Earth’s Twin”, Venus is the second closest planet to our Sun – ranging from 107,477,000 km at perihelion to 108,939,000 km at aphelion. An Earth day is 24 hours no matter what planet you are on. the time it takes a planet to rotate once relative to the stars, and the solar day, the time it takes for the sun to return to the same position in the sky. Mars has the third longest at 24 hours, 37 This is called a sidereal day. "Sunrise to sunrise" is a rough definition of the solar day. Rotation of Planets: You might know that all of the planets in our solar system rotate, which means that they are spinning around. Which Planet has the Longest Day? Load More Planetary Science Science Seasons Astronomy South Africa Deserts Calendar Planet Mercury Question: Which planet in our solar system has the longest day? Planet Mercury has the Longest Day. After Venus, Mercury has the second longest day taking 58 Earth days, 15 hours, 30 mins and 14 secs. Its day lasts longer than its orbit.