What Planets Have The Longest And Shortest Days In The Solar System?

There are 24 hours in a day on Earth, but other planets within our solar system have different lengths of days.

Some have shorter days, while others have longer days.

What Planets Have The Longest And Shortest Days In The Solar System

Space is fascinating and every planet is so different from the other, and we guess you could say that… every day is different!

This post is going to explain everything surrounding the longest and shortest days in our solar system.

Key Things To Remember

The length of a day depends upon how far away from the Sun the planet is, as well as the planet’s mass.

Typically, the nearer a planet is to the sun, the faster it rotates around its axis.

This means that the side facing the sun will be hotter than the opposite side.

As a result, the temperature difference between the two sides causes air pressure differences which cause winds to blow across the surface of the planet.

These winds then carry heat energy away from the hot side of the planet towards the cooler side.

This process continues until there is no more heat available for wind flow and the planet reaches thermal equilibrium with the surrounding environment.

The time taken for this to happen is known as the planet’s rotation period.


Mercury’s year is shorter than our year, but it spins more slowly. This means that there are five Mercury days per Mercurian year.

People living on Mercury would experience one full day of sunlight every two years. Mercury spins once on its axis in 58.6 Earth days.

Although that may seem like a long time, consider that its year is only 88 Earth days long! This is due to its close orbit around the Sun.



On Venus, one day lasts nearly 243 Earth days due to its slow rotation on its axis. Planets closer to the Sun have a shorter year.

In other words, Venus residents would only see two sunrises a year because the day is longer than a year.

The planet Venus spins “backward” on its axis, which means that Venus’ sunrise and sunset occur in different directions.


Mars’ day length is very similar to Earth’s at 24 hours and 37 minutes, which is one reason it’s considered to be Earth’s twin planet.

Mars also has a longer year than Earth, as it’s further away from the sun — we’re talking 323 days longer, to be precise!


It is much more difficult to determine the “day length” of gas giant worlds.

There are no solid surfaces on the outer worlds, but their cores are solid and covered with layers of clouds and layers of liquid metallic hydrogen and helium.

On Jupiter, the equatorial region of the cloud belts rotates every 9 hours and 56 minutes, while the poles rotate every 9 hours 50 minutes.

Jupiter has a 9 hour, 55 minute day, as determined by its magnetic field’s rotation rate. This is the “canonical” length of a day on Jupiter.


Known for the famous rings encircling around the planet, measurements of the magnetic field and cloud layers of the gas giant Saturn were taken by the Cassini spacecraft.

Saturn has an official day length of ten hours and 33 minutes, according to planetary scientists.


There are many strange aspects to Uranus.

The most unusual thing about Uranus is its tilted over position, which allows it to revolve around the Sun on its side.

During part of its 84-year orbit, one or both axes point toward the Sun.

Every 17 hours and 14 minutes, the planet rotates on its axis.

As a result of the length of the day, the length of the Uranian year, and the weird axial tilt, a day on this planet is as long as a season.



On the gas giant planet Neptune, a day lasts approximately 15 hours.

The rotation rate of this gas giant took scientists a number of years to calculate.

Studying images of the planet as features rotated in its atmosphere enabled them to complete the task.

Since Voyager 2 in 1989, no spacecraft has visited Neptune, so its day can only be studied from the ground.


At 248 years, Pluto’s year is the longest of all known planets as of now, and at six Earth days and 9.5 hours, Pluto also has a fairly long day.

Pluto is lying on its side at 122 degrees angle with the Sun.

The result is that, during part of Pluto’s year, portions of its surface are either in continuous daylight or in constant darkness.

Which Planet Has The Longest Day?

The correct answer is Mercury.

Mercury completes a full rotation on its axis every 58 days or so, meaning a Solar Day on Mercury lasts for two orbits, or 176 days.

The people who say Venus are basing it on the sidereal rotation rather than the length of the day, which we use.

Negative sidereal rotation is caused by the planet rotating in the opposite direction to Earth.

This is thought to be caused by the object being hit early when the solar system was being born.

It won’t slow down and then spin in the opposite direction once it spins in the opposite direction.

If we were to base our question on the sidereal rotation of Venus, then it would indeed be the planet with the longest day, with a standard rotation taking 243 Earth days, which is an incredibly long time.

Considering the duration of a single Venusian axial rotation, it’s really small wonder that it has shorter years than days.

Disregarding the sidereal rotation of Venus, a single solar day takes 117 days, which isn’t quite enough to pip Mercury.

Which Planet Has The Shortest Day?

Jupiter may be the largest planet in our solar system, but it’s by no means sluggish.

This gas giant completes a full rotation in roughly 9.9 hours, which seems nuts, but, actually, those with the shortest days are the gas giants, while those with the longest are the rocky planets such as the Earth.

What Planet Has The Longest Year?

The longest year belongs to Neptune, which has 164.77 Earth years in its year.

It is the farthest planet from the Sun, thus, it’s moving slower and has a longer distance to cover.

What Planet Has The Shortest Year?

Mercury may take the longest day title, but it also brings home the shortest year award — weird, right?

As it’s the closest planet to the sun, in terms of orbital velocity, it’s traveling the fastest by a long way.

Why does proximity to the same have an impact on orbital speed? Well, it all comes down to exposure to gravitational force.

The closer a planet is to the sun, the more it “feels” the effect of the sun’s gravity, resulting in the planet being slingshotted around its orbit at super high speeds!


Having read all this information we have provided you with, you should now understand what planet has the longest day and what planet has the shortest day.

All this is very interesting stuff, and took years of research from scientists to get the correct answer for each planet in our solar system.

Gordon Watts