Bill Arnett:

I had an interesting view of The King this evening.

The seeing was not very good but I was able to see the Europa shadow preceeding the GRS and another dark apparition following the GRS. That apparition looked almost exactly like Europa's shadow but perhaps a bit smaller. The seeing wasn't good enough to distinguish any size or shape. But it was in exactly the position that should have been occupied by Ganymede in transit.

My theory is that the dark spot I saw was the thin crescent of the dark side of Ganymede. Did anyone else see this?

Peter Natscher:

While at Montebello (last night) I too noticed that little dark spot matching Europa's shadow in size, following the GRS. At one point in time there were Europa's shadow, followed by the GRS, then the other black spot, and lastly Ganymede all moving along from east to west across Jupiter's face. What a show!

I was observing with my Ceravolo HD216. The sky in general was very clear, but soft due to air turbulence. Even though the detail came and went observing Saturn, I was lucky enough to see Mimas--a moon of Saturn I hardly ever get to see from my house. It's elusive for any scope under 10" aperture to spot, due to its being so close to Saturn, and being faint (mag. 12). It orbits Saturn closely just outside Ring A.

I lost my battery power after four hours running. I'm wondering if the 40°F temp killed my 12V battery? It was recharged (24 hrs) just two weeks ago. Does anyone know if this is common. I think I'll buy a 20' cable to power up from my car in case this happens again.

Montebello was cold last night, but dressed properly, the observing session was enjoyable. The key to enjoying colder weather (40°F) with windchill is to layer clothing (wool), wear head covering, gloves, and wear boots that 'insulate'. Thin shoes or running shoes will let your feet freeze.

Bill Arnett:

Huh? You [Peter] saw *both* the extra black spot *and* Ganymede as separate objects? That blows my theory that the spot was the dark crescent of Ganymede. Are you sure you weren't seeing a white oval instead of Ganymede?

Starry Night says Mimas is 12.8. If you saw it, then Enceladus at 11.6 must have been easy :-) I've seen Enceladus from my backyard but never Mimas.

Akkana Peck:

It was indeed a strange sight (in Bill's 12"; I couldn't see either dark spot in my 80mm f/7 achromat or in a nearby 4.5" Newt). It was hard to be sure in the extremely unsteady seeing, but as far as I could make out, both spots looked very black and very round. I've never seen a moon stand out that blackly before, especially when standing against a dark band. And I wouldn't expect the crescent of the "dark side" of Ganymede to be that obvious (even though Ganymede is a big moon).

Peter Natscher:

I saw a darker spot (smaller than Europa's shadow) following the GRS as it rounded Jupiter's eastern limb. This was while Ganymede was still off Jupiter's limb, ready to transit. By the time Ganymede was inside Jupiter's darker limb, looking like a white wart on Jupiter's face, the three objects (Europa's shadow, GRS and the other dark spot) were merrily following eachother westward across Jupiter's face.

I can never see Mimas from my driveway--too much temp. instability and light pollution in my neighborhood. I can barely see Enceladus from there. Last night provided good enough transparency for me to clearly see Enceladus and Mimas as the wind died down at 10 p.m. Turbulence cuts down on magnitude gain.

Bill Arnett:

This is very interesting. What do you suppose the other dark spot was? It was certainly not Ganymede's shadow. Did you see the dark crescent of Ganymede itself, too? Do you remember the distance relationships? My recollection, consistent with what Starry Night shows, is that at about 7:30 when the GRS was near the meridian the GRS was just slightly closer to Europa's shadow than the other dark spot which is where Ganymede was. Your dark spot must have been closer to the GRS; how much?

My observation of the "other" spot was that it was very dark, like a shadow. I've never seen a jovian atomspheric feature anywhere near that dark. I suppose it could have been a shadow from Amathea but that's a stretch -- Amalthea is only about 180 km in diameter, its shadow would be about the same size, I guess, awfully small to be seen from here.

Akkana Peck [to Peter]:

What time were you looking? It looks to me like Ganymede and Europa's shadow should have become visible about 5:50, with Ganymede hanging just off the limb, and Ganymede should have hit the limb about twenty minutes later (with the Europa shadow still very close to the limb). But the GRS wasn't visible yet at that point.

I was looking at about 7:40, and one dark spot was on one side of the GRS, the other one on the other side (which seems right if one was Europa's shadow and the other was Ganymede, judging by my applet; the Y coordinates for the moons are inverted, as Peter pointed out to me a while back and I haven't fixed yet, but I think the X coordinates are right since they usually agree with other astro programs).

Peter Natscher:

At around 6 p.m., Europa egressed from transit and its shadow ingressed on the other side of Jupiter. After half an hour, the GRS started appearing following Europa's small shadow as it moved along out in front of the GRS. As Europa continued to move west, away from Jupiter's limb, its shadow and the GRS moved west and Ganymede approached the eastern limb of Jupiter, next to make a transit ingress. Ganymede is so much larger than Europa, it was easily followed well into its transit of Jupiter, even though Ganymede has a lower albedo than Europa (0.34 vs. 0.60).