A large dark oval feature about 10 000 × 5000 km in the clouds of Neptune, photographed by Voyager 2 in 1989. It lay at about 20° south latitude and appeared to consist of a huge rotating vortex, similar to Jupiter's Great Red Spot. However, the Great Dark Spot was not visible to the Hubble Space Telescope in 1994, having apparently dispersed. Since then, other similar features have been seen in the northern hemisphere of Neptune.
Subjects: Astronomy and Astrophysics.