Ananke, or Jupiter XII

Ananke was not discovered until 1951 and was known only as Jupiter-XII until it was given its official name in 1975. Probes sent to Jupiter have since revealed Ananke to be 29 km in diameter and it rotates on its axis every 8.3 hours. When these images were created it was at magnitude 18.7.

To form the images above, 60 exposures were taken with a total duration of 1780 seconds. The satellite was moving with respect to the background stars during this time so the sub-images were in two different ways. In the left-hand image the subs were stacked on the stars, so that Ananke is trailed. In the left-hand image the subs were stacked on the predicted motion of the satellite, not on the stars themselves. In consequence, Ananke shows up as a fairly sharp circular object whereas all the stars are now trailed slightly.