Neptune and Its Moons


This movie was put together using 70 days worth of solar system observations from the Kepler spacecraft taken during its reinvented “K2” mission. The planet Neptune appears from the left on Day 15, followed by its moon Triton, which looks small and faint. Sharp-eyed observers may also spot Neptune’s tiny moon Nereid at Day 24.

Neptune doesn’t actually move backward in its orbit, but it appears to do so because of the changing position of the Kepler spacecraft as it orbits around the sun. The same sort of retrograde motion is seen in the movement of the outer planets over the course of a year as viewed from Earth.

[youtube https://www.youtube.com/watch?v=Tw-q3uM_5_0]

Video Credit: NASA

Neptune, Triton, Rings, and Stars


Neptune-South-Pole-Voyager-2_950x682Voyager 2 took the images used to produce this picture of the Neptunian system as it was outbound from the planet on 25 August, 1989. Cruising through the outer solar system, the Voyager 2 spacecraft made its closest approach to Neptune on August 25, 1989, the only spacecraft to visit the most distant gas giant. The image captures the planet and Triton as thin sunlit crescents. A close look shows cirrus clouds and a dark band circle Neptune’s south polar region, with a cloudy vortex above the pole itself. (Pole is just past 6:30 on the planet in this orientation.) Parts of the very faint ring system that was discovered during the Voyager 2 flyby are also visible. The background starfield is composed from sky survey data centered on the constellation Camelopardalis, corresponding to the outbound Voyager‘s point of view.

Image Credit: NASA

Approaching Neptune and Triton


This montage of images taken by Voyager 2 shows Neptune as it would appear from a spacecraft approaching Triton, Neptune’s largest moon. (Click on the picture to embiggen.) The eroded south polar cap of Triton is shown at the bottom of Triton’s image. Cryovolcanic terrain is at the upper right, and the as-yet unexplained “cantaloupe terrain” is at the upper left. Voyager 2 flew by Triton and Neptune in 1989.

Image Credit: NASA

Double Crescent


The Voyager 2 spacecraft camera captured Neptune and Triton together in crescent phase as it passed by in 1989. This picture of the gas giant and its cloudy moon was taken from behind the planet just after closest approach. It could not have been taken from Earth because Neptune never shows a crescent phase to sunward Earth; the sun always fully illuminates Neptune from our point of view. The unusual vantage point robs Neptune of its familiar blue color because the sunlight seen from behind the planet is scattered forward and is reddened like the setting Sun.

Image Credit: NASA/Voyager 2