Not all the days, in the planets of the solar system, have the same duration, as a day corresponds to the time that a planet takes in doing a complete turn onto its axis. All the planets have a different day duration from ours, and the duration of their year also variates a lot.
Jupiter, with a distance to the Sun much greater than the Earth’s, is the biggest planet of the solar system. It is also the planet with the densest atmosphere, and, even if the mass of the planet is 300 times greater than the Earth’s, its volume multiplies itself by 1 300 times.
We could think that because it is the biggest planet of the solar system, this one would have a very low rotation speed, and, consequently, a day that would last a lot. However, its rotation period is of 9 hours and 50 minutes. Therefore, the duration of the days on a planet, hasn’t anything to do with its distance to the Sun, but with its rotation movement and its inclination axis. The thing that is related to the distance to the Sun is the duration of the year. A year on Jupiter lasts for 11,86 terrestrial years.
In the case of Saturn, the days are quite difficult to measure. In this case Saturn we haven’t got a reference point from which we could measure the duration of a day. In these cases we normally use the magnetic field of the planet. Even so, here we also find ourselves with a problem. In fact, Enceladus, one of its moons, doesn’t stop sending geysers, that when throwing material into space, interact with the planet’s magnetic field. For this reason, we can neither have very clear the duration of Saturn’s rotation using this method.
Therefore, the only thing we can affirm is that the duration of a Saturn’s day is estimated at 10 hours and 50 minutes. What we can know exactly is the duration of its year: 29,5 terrestrial years.
In Uranus, one of its poles is always pointing to the Sun, as its rotation axis is inclined almost in its totality in relation to the Sun. However, we can say that the duration of the days on Uranus is of 17 hours and 14 minutes in making a complete turn onto its axis. Even so, if we understand a day as the time-lapse from the sunrise until the sunshine, we find ourselves with a day on Uranus that lasts for 84 years, the same time that takes the planet to complete its orbit around the Sun.
Finally we have Neptune, the furthest planet from the Sun. Neptune takes 16 hours, 6 minutes and 4 seconds in making a turn onto its axis, a little less than Uranus. A year on that planet has a duration that is equivalent to 165 terrestrial years.
Neptune has an inclination axis of 28,32º (very similar to the Earth’s and Mars’), reason for which it also experiences its own seasons.