|Part of the Solar System|
Neptune, the outermost of the planets, was predicted mathematically by its effects on the orbit of Uranus. For this reason, its discovery in 1846 was a great triumph for Newtonian mechanics.
It is the densest planet of the gas giants and it features the fastest winds of any planet in the Solar System, with speeds reaching nearly 600 m/s (1340 mph). Neptune’s orbital period lasts 165 years, meaning that since the planet’s discovery, it has only completed one orbit (in July 2011).
Though not conventionally visible to the unaided eye, Neptune can be seen as a small blue disk in telescopes (2.2 to 2.4 arcseconds in size). An experienced observer may also be able to discern Triton, the largest satellite of Neptune. Despite the moon’s vast distance from Earth, Triton’s high albedo (0.76) allows for an apparent magnitude (13.5) brighter than any of the Uranian moons. Notably, Triton is the only large moon that exhibits a retrograde orbit. It is also thought to be a captured Kuiper belt object.