Neptune from Triton. Illustration of a view from the surface of Triton, the largest moon of the planet Neptune (seen as a crescent at centre right). The Sun is at upper left. Neptune, the eighth planet from the Sun, has a diameter of over 48,000 kilometres and orbits at an average distance of 4.5 billion kilometres. It is considered an ice giant, with an icy interior and an atmosphere of hydrogen and helium. Triton, its largest moon, consists of ices and rocks. It has a diameter of around 2700 kilometres, and orbits Neptune at a distance of around 355,000 kilometres. Seasons on Triton have been observed using the CRIRES (cryogenic high-resolution infrared echelle spectrograph) instrument on ESO's Very Large Telescope.