The one that is the biggest distance away, that's Neptune 164 years, but dwarf planet Eris takes 550 years.
Around its axis is a day. Around its orbit is a year.
The time a planet takes to make a single trip around the sun is called its orbital period or year.
Technically, since Pluto is no longer a planet, but a dwarf planet, Uranus is the planet that takes the longest to orbit the sun.
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Period of rotation
Neptune takes the longest as it is the farthest away.
It takes one year for us to make a revolution around the Sun.
The time it takes for any given planet to make one complete revolution around its sun determines the length of its year.
Because the farther away a planet is from the sun the bigger its orbit is and that will make a revolution longer.example: Neptune is the farthest planet from the sun and it takes 164 earth years to revolve around the sun and Mercury is the closest planet from the sun and it takes 88 earth days to revolve around the sun.
For a planet in our solar system, one revolution around the Sun is called a "year." Each planet has a different year. As you know, Earth takes 365.25 days to follow its orbit around the Sun, though Jupiter's year is about 4335 earth days. It all depends on how long it takes each one to revolve around the Sun.
The revolution period for Mercury, which is the time it takes to orbit around the Sun, is about 88 Earth days. Mercury has a highly elliptical orbit, so its distance from the Sun varies during its revolution.
It takes approximately 88 Earth days for the planet Mercury to complete one revolution around the Sun.