Astrometry of Jupiter's Outer Satellites
I've had a long time interest in observing faint outer satellites of the major planets. For example I observed Phobos & Deimos visually in 1990 and later imaged them at the opposition of Mars in 2005. My first image of any faint satellite was taken on film of 14th mag Himalia (Jupiter VI) on 16th February 1991. I took measurements of the photograph which confirmed the find and the photo was published in Sky & Telescope in February 1993. CCD's really opened up the possibilities and so in 1999 I targeted as many of Jupiter's outer satellites as possible in one observing session on the 4-5th October. I didn't have a GOTO system at that time and so the fields near Jupiter were manually identified from star charts. The images were all measured using COAA SX software with reference to the Guide Star Catalogue. Short exposures of 3-11 minutes were used. Glare from Jupiter wasn't a problem as the satellites were all over a degree away from Jupiter. Pasiphae was the furthest angular distance from Jupiter at 2.8 degrees.
Results
| Measured | JPL Horizons | Difference (Arc sec) |
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| Satellite | Mag | Time UT | RA h:m:s | DEC d:m:s | RA h:m:s | DEC d:m:s | RA | DEC | |
| Himalia | 14.65 | 22:47 | 2 00 19.10 | +10 06 52.4 | 2 00 19.09 | +10 06 51.5 | +0.15 | +0.9 | |
| Lysithea | 18.14 | 22:47 | 2 00 44.93 | +10 03 04.5 | 2 00 44.91 | +10 03 04.0 | +0.30 | +0.5 | |
| Elara | 16.60 | 23:17 | 2 07 30.54 | +11 02 41.1 | 2 07 30.56 | +11 02 42.0 | -0.30 | -0.9 | |
| Pasiphae | 16.82 | 23:50 | 1 51 20.29 | +10 30 14.4 | 1 51 20.38 | +10 30 14.1 | -1.35 | +0.3 | |
| Carme | 17.65 | 21:25 | 1 48 54.54 | +09 03 31.4 | 1 48 54.53 | +09 03 32.1 | +0.15 | -0.7 | |
| Sinope | 17.96 | 00:00 | 2 08 14.14 | +12 13 06.7 | 2 08 14.05 | +12 13 06.4 | +1.35 | +0.3 | |
| Ananke | 18.78 | 00:29 | 2 12 19.70 | +10 23 58.7 | 2 12 19.77 | +10 23 59.5 | -1.05 | -0.8 | |
Other Satellites
Imaging and identification of fainter satellites should be possible now with better CCD's and imaging technique but the next possible target of Jupiter's realm is Leda at magnitude 20. Saturn's faint satellites aren't much easier, I took this image of Phoebe on 21st January 1999, Phoebe was an easy target at magnitude 16.6 and 0.5 degree away from Saturn but next up is probably Helene at magnitude 18.4. Helene orbits a little closer in than Dione so glare will make detection difficult.
This mosaic was made to include Saturn and Phoebe in the view. The image of Saturn is overexposed, an internal reflection is seen below the overexposed image.