This image was captured by the Voyager 2 spacecraft as it flew past Neptune on it's way out of the solar system. It was taken from 'behind' Neptune (the side away from the Sun), and is unique in the sense that it could never have been taken from the Earth. Neptune can never show a crescent phase towards the Earth, as we are on Neptune's sunward side. Another interesting fact is that Neptune does not have it's familiar blue color from behind, as the sunlight passing through it's atmosphere is scattered forward, rather than back, so it is reddened.