neptune

Neptune (pronounced /ˈnɛptjuːn/) is the eighth and farthest planet from the Sun in the Solar System.
It is the fourth largest planet by diameter, and the third largest by mass.
Neptune is 17 times the mass of Earth and is slightly more massive than its near-twin Uranus, which is 15 Earth masses and less dense.

The planet is named after the Roman god of the sea.

Urbain Jean Joseph Le Verrier and John Couch Adams are the first to discover and demonstrate the presence of planet Neptune, using only mathematics and astronomical observations of the known planet Uranus. Actually both of them demonstrated the presence of planet Neptune in approximately the same time, without knowing each-other .

Johann Gottfried Galle was the first person that actually viewed the planet Neptune. He used the calculations of Urbain Le Verrier to know where to look.

From its discovery until 1930, Neptune was the farthest known planet. Upon the discovery of Pluto in 1930
In 2006 an IAU resolution created a new official definition for the term "planet".
From that point onwards Neptune is again the last planet from our Solar System.