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.
|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|
|Exposure||1708s in 31 subs.|
|Centre of image||RA 19h17m02.5s Dec -22°44'50"|
|Image dimensions||3.9 arcmin × 2.2 arcmin|