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Neptune has the third longest year in our solar system, lasting about 165 Earth years. Uranus has the second longest year, lasting about 84 Earth years, while Saturn has the longest year, lasting about 29 Earth years.
Pluto has the longest year, if it was still a planet that is, equal to 248.76 Earth years. Since Pluto is no longer considered a planet, the planet with the longest year is Neptune, at 164.8 Earth years per revolution around the Sun.
A year on another planet is determined by its orbital period around the sun. For example, a year on Mercury is about 88 Earth days, while a year on Mars is about 687 Earth days. The length of a year on a planet depends on its distance from the sun and how fast it orbits.
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One year on the planet Neptune is the equivalent of 164.79 years on Earth. A day on Neptune is equal to 16 hours and 6 minutes.
The dwarf planet Pluto is the planet with a year 248 earth years long.
The dwarf planet Haumea is the planet with a year 280 earth years long.
The dwarf planet Makemake is the planet with a year 310 earth years long.
In our solar system Neptune is the planet with the longest period or year - equal to about 165 Earth years.
The dwarf planet, Pluto, has a year of 247.9 Earth years.
Now that Pluto has been downgraded to a dwarf planet, Neptune is the most distant planet from the Sun. It takes 164.79 Earth years for Neptune to circle the Sun, so one Earth year would be about 1/165 of a Neptune year (the time it takes Neptune to circle the Sun).
One Saturn year is equal to about 29.5 Earth years.
No planet has. (Planet Saturn has a year lasting about 29 Earth years.)