Themisto, or Jupiter XVIII


Themisto was discovered in 1975 and promptly lost until 2000. It is a rather small body, only 9km in diameter, and never gets brighter than 20th magnitude.

In the image above, Themisto is indicated by cross bars. The arrow points at Gaia EDR3-6771111466513671680 which is catalogued at g=20.66. Themisto itself was magnitude V=20.3 when this image was taken.

Image information
Date and time of observation  2020-09-05 22:40 UT
Telescope 0.4m f/6.5 Dilworth-Relay
Camera Starlight Xpress Trius-PRO SX814 CCD
Filter None
Exposure 1708s in 31 subs.
Centre of image RA 19h17m02.5s  Dec -22°44'50"
Image dimensions 3.9 arcmin × 2.2 arcmin