Neptune's Great Dark Spot
Date: 23 Aug 1989
This image shows the closest face-on view of Neptune's Great Dark Spot captured by the Voyager 2 spacecraft during the only visit to the most distant of the eight major planets in our solar system.
The smallest structures that can be seen are of an order of 50 kilometers (31 miles). The image shows feathery white clouds that overlie the boundary of the dark and light blue regions.
Original caption is available here.