Jupiter shadow transits and smaller scopes

[Pixies]

I was out with my Vixen SD81S tonight and saw that there was a shadow transit of Europa. So I swung over to the east, stuck in a 5mm eyepiece  (for x125 magnification) and watched.

Now, the local seeing  over rooftops was pretty poor and at first I couldn't see anything. But I persevered and could start to make out a faint tiny grey dot where the shadow was expected. Not the pin-sharp black speck I'm used to in  my bigger scopes. I assume this is down to the seeing and possibly the shadow was beyond the  resolving power of the 81mm aperture.

What are your experiences with shadow transits and smaller scopes? Was my experience typical or was it down to poor seeing? Perhaps a bit more magnification? Does the moon size make any difference?

 

Cheers

[Sunshine]

I believe what you're describing can be attributed to poor seeing, a transit shadow is a small target and would appear more dark and refined in larger scopes. In my time with my 100mm I have only seen a handful of transits under good seeing, though I don't know what the limit of "small" scopes is you're referring to, I have managed to see a sharp black pinpoint on occasion and not so sharp on others.

[John]

I've just been observing tonights Europa shadow transit. With my 100mm refractor the shadow was quite small and low on Jupiter's disk. Not as easy to see as some transit shadow's I agree. I found 150x showed the sharpest view tonight. The shadow did appear black but that is with more aperture.

Your Vixen SD81S (and your eye) are doing a good job 🙂

Edited September 26, 2023 by John

[IB20]

I’ve viewed multiple transits through 76 and 80mm scopes and I tend to get a jet black spot for all four moons. No doubt your Vixen would yield similar results and I’d attribute what you experienced last night to the seeing coupled with a fairly low transit across the southern hemisphere. Sometimes dropping the mag to around 90-100x will help sharpen things up a tad in iffy seeing. 

I recall a double transit of Ganymede and Europa where the seeing was dire with poor transparency and Europa would frequently appear a soft grey in comparison to Ganymede’s larger and darker spot. 

Edited September 26, 2023 by IB20

[Stu]

Europa’s shadow is a fair bit smaller than Io’s (for example), because it orbits further out. That does make it trickier to pick up and with poor seeing that would likely explain it. I’ve seen shadow transits in scopes down to 60mm but they aren’t always easy to see in smaller apertures.

One other thing worth looking out for are transits of Ganymede and Callisto. These have lower albedo than Io and Europa so they appear dark against the Jovian surface, rather than bright. They are more grey than black and have slightly fuzzy edges rather than the sharp, jet black ovals of the shadows. I recall (vaguely!) seeing a triple shadow transit with a Callisto (or Ganymede!) transit in poor seeing, so there were four dark spots to be seen, one slightly less black.

 

[Nik271]

Europa is the smallest of the Galilean moons and naturally  casts the smallest shadow. This has also been my experience observing it. Io and especially Ganymede's shadows are much more obvious to spot. Incidentally I have not observed a shadow transit by Calllisto.

[Bugdozer]

I have observed a shadow transit of Io in my Celestron 5se with 9.7mm eyepiece, so around 130x magnification. I wasn't sure if that was what I was really seeing or if my eyes were playing tricks. I didn't know in advance there was a transit happening so I looked it up when I went back in and was quite pleased I wasn't imagining it.