Neptune.
Neptune
The planet that was farthest from the Sun from February 7, 1979 until February 11, 1999 was Uranus. Though Pluto was considered the outermost planet in the solar system since its discovery, its highly elliptical orbit sometimes brought it closer to the Sun than Uranus.
Mercury has always been the closest planet to the Sun and unless a little rogue planet slipped in between, during 1999, then Mercury is still the closest to the Sun
Pluto used to be the outermost planet, except that sometimes it became Neptune because Pluto's elliptical orbit is far from circular. From 1979 to 1999 Neptune was the farthest planet from the Sun and remains the farthest from the Sun today, because Pluto us no longer defined as a planet.
Gas Giants
Uranus is the seventh planet from the sun and was discovered in 1781.
Uranus is the second furthest planet from the sun. Neptune, now the furthest planet from the sun, was the second furthest planet from the sun after Pluto was discovered in 1930 until Pluto was reclassified as a dwarf planet in 2003.
Uranus is the second furthest planet from the sun. Neptune, now the furthest planet from the sun, was the second furthest planet from the sun after Pluto was discovered in 1930 until Pluto was reclassified as a dwarf planet in 2003.
Pluto
Neptune's orbit is more elliptical than Pluto's, causing their orbits to sometimes intersect. From 1979 to 1999, Neptune's elliptical orbit brought it closer to the sun than Pluto, making Neptune the farthest planet from the sun during that time.
neptune
Back in 1999, Pluto was still a planet, but was nearer to the Sun than Neptune was from1979 to1999. Pluto's orbit is fairly eccentric; during parts of its orbit, it is nearer to the Sun than Neptune is. So, answer: Neptune was farthest, but it became Pluto again some time in 1999.