Lysithea, or Jupiter X


Lysithea was not discovered until 1938 and was known only as Jupiter-X until it was given its official name in 1975. Probes sent to Jupiter have since revealed Lysithea to be 42 km in diameter and it rotates on its axis every 12.8 hours. When this image was created it was at 18.3 magnitude.

To form the image above twenty exposures were taken, each of 1 minute duration. The satellite was moving with respect to the background stars during this time so the sub-images were stacked on the predicted motion of the satellite, not on the stars themselves. In consequence, Lysithea shows up as a sharp circular object whereas all the stars are trailed slightly.

Image information
Date and time of observation  2020-08-05 22:05 UT
Telescope 0.4m f/6.5 Dilworth-Relay
Camera Starlight Xpress Trius-PRO SX814 CCD
Filter None
Exposure 20×60s median-stacked on predicted motion of the satellite
Centre of image RA 19h27m43.7s  Dec -21°59'35"
Image dimensions 8.3 arcmin × 5.3 arcmin