How long is a year on other planets compared to Earth? Here is the duration from Mercury to Uranus

Although a year is coming to an end for Earth, the same cannot be said for the other planets in the Solar System. The planets do not all orbit the Sun at the same rate: la Kepler’s third law in fact he states that the square of the revolution period of an object around the Sun is proportional al cube of its semi major axis. Translated, the further an object is from the Sun, the more time it takes to orbit it. Mercurywhich is the closest planet to the Sun (about 58 million km) takes only 88 Earth days to rotate around our star, Mars takes some 687while Neptune, the most distant of the planets, takes approx 165 Earth years to complete an entire orbit.

It is therefore possible to establish how long does a year last on Mars and the other planets in reference to the length of the year (and day) on Earth. To do this it is necessary to distinguish thesidereal yearunderstood as the period necessary for the Earth to complete an entire revolution around the Sun returning to the same point of the orbit with respect to the fixed stars, from that solarunderstood as the orbital period to return to the same position around the Sun. For the Earth, the sidereal year lasts 365 days, 6 hours, 9 minutes and 9.54 secondswhile the solar one 365 days. The 366-day leap years are introduced to accommodate this discrepancy.

Likewise every planet rotates around its axis with a different time than that on Earth, so a day on Earth is not equivalent to a day on Mars for example. Always distinguishing between sidereal day (two consecutive passages of the same star across the meridian) e solar (two consecutive passages of the Sun at the meridian), the days on the various planets can go from 9 hours of Jupiter to 244 days of Venusin a paradoxical situation in which on Venus a day lasts more than a year. So let’s see in this article how long a sidereal year and day lasts for each planet in the Solar System.

Mercury, 88 Earth days

The first planet in order of distance from the Sun, Mercuryis also the one which, as predicted by Kepler’s laws, has the shortest period of revolution around the Sun. Mercury presents ahighly eccentric orbit which leads it to vary its distance from the Sun from 46 million km in perihelion to 67 million km in aphelion, with an average distance of 57.91 million km. A year on Mercury it lasts 87.96 Earth dayswhich is the time it takes for the planet to complete a complete orbit around the Sun returning to the same position with respect to the fixed stars (sidereal period). Mercury is also in orbital-rotational resonancecompleting three rotations around its axis every two orbits around the Sun, are in fact necessary 58.65 Earth days to make Mercury perform a revolution on itself.

Venus, 225 Earth days

The second planet from the Sun, Venusbeing more distant from Mercury, will also have a longer orbital period. The average distance of Venus, equal to approximately 108.21 million kmimplies for Kepler’s laws that a sidereal year on Venus lasts 224 days 16 hours and 48 minutes. Curiously, probably due to the effect of a large meteor impact, Venus rotates on itself approximately 243.69 Earth days. Consequentially, a Venusian day lasts longer than a Venusian year! Furthermore, Venus rotates in clockwise (retrograde), so an observer on its surface would see sunrise in the west and sunset in the east.

Mars, 687 Earth days

The red planet, Marsbeing further from the Sun than Earth, will orbit around our parent star with a sidereal period greater than that of our planet. Mars in fact, distant on average 227.94 million kmcompletes a complete rotation around the Sun in approximately 686.96 Earth daysequal to one year, 320 days and 18.2 Earth hours. A day on Mars it is very similar to that on Earth, lasting in fact 24 hours, 37 minutes and 23 seconds. Mars also has an inclination of the rotation axis similar to that of Earth, thus resulting in a system of seasons similar to ours, but with double the duration.

Jupiter, 12 Earth years

The largest planet in the Solar System, Jupiteris so far from the Sun that its orbital period is no longer counted in days, but in Earth years. In fact, they are on average distant 778.41 million km from the Sun, a year on Jupiter lasts 4,333.28 days or 11.86 Earth years. The gas giant rotates very quickly around its axis, in fact a Jovian day lasts only 9.92 hours. This high rotation speed generates a equatorial bulge due to the high centripetal acceleration at the equator, a bulge visible even only with an amateur telescope. Having a rotation axis tilted by only 3 degrees, Jupiter does not experience significant seasonal variations like Mars and Earth.

Saturn, 29 Earth years

The Lord of the Rings, Saturn, is at an average distance from the Sun 1.43 billion kmemploying 29.45 Earth years to complete a complete orbit around our star. This value relates the Saturnian year to the Jovian year, given that the latter corresponds exactly to two fifths of Saturn’s orbital period, generating a orbital resonance of 5:2. Saturn also rotates very quickly around its axis, in fact a day on Saturn it only lasts 10.56 hours. Every 15 years, Saturn is found at certain points in its orbit for which the characteristics rings they come to meet perfectly cut when observed from Earth. This event will happen in 2025, November 8th to be exact.

Uranus, 84 Earth years

The gas giant Uranus is on average 2.87 billion km from the Sun and a year on this planet lasts approximately 84.01 Earth years. Uranus rotates around its axis in less than 24 hours, 5.24pm to be exact, and it does so in clockwise (retrograde motion), so, as on Venus, an observer would see the sunrise in the west and the sunset in the east. One of the peculiar characteristics of Uranus is that it orbits the Sun, practically on its side. His rotation axis in fact it is inclined of approx 90 degreesprobably as a result of a collision with another object, thus exposing one of its poles to the Sun for half the revolution period.

Neptune, 165 Earth years

The last planet in order of distance from the Sun is Neptunewith an average distance from our star of approximately 4.49 billion km. Such a distance also means that Neptune has the period of revolution around the Sun longer of all the planets in the Solar System. In fact, a year on Neptune lasts 164.88 Earth yearsso long that since its discovery in 1846, Neptune was able to accomplish a single orbit around the Sun, which happened between 2010 and 2011. Neptune rotates around its axis in 16.11 hourswith an axis inclination of 28.32 degrees, similar to Mars and Earth, experiencing seasonality similar to the aforementioned planets but with a duration of each season of 40 years.

Summary table