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