The image, above, is a composite of 4 images recorded by NASA’s Voyager spacecraft as it flew by Neptune on it’s way out of the solar system about twenty years ago.
The information quoted, below, is taken from the APOD for 16 January 2014.
[[ “Explanation: Despina is a tiny moon of Neptune. A mere 148 kilometers across, diminutive Despina was discovered in 1989, in images from the Voyager 2 spacecraft taken during its encounter with the solar system’s most distant gas giant planet. But looking through the Voyager 2 data 20 years later, amateur image processor and philosophy professor Ted Stryk discovered something no one had recognized before — images that show the shadow of Despina in transit across Neptune’s blue cloud tops. His composite view of Despina and its shadow is composed of four archival frames taken on August 24, 1989, separated by nine minutes. Despina itself has been artificially brightened to make it easier to see. In ancient Greek mythology, Despina is a daughter of Poseidon, the Roman god Neptune. ]]
The image is reminiscent of Moon Shadows on Jupiter that I posted a few months ago except that today’s post shows a composite of 4 images of the single moon, Despina, and the shadow she casts on Neptune rather than a single image showing multiple moons and the shadows they cast on Jupiter.