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My friend Rafael Compassi has noticed that whenever he catches the Galilean satellites the tendency to appear dark central spots in Callisto and Ganymede is frequent. This led us to wonder if these spots could be an inherent consequence of capture, or even some processing defect, since they usually always manifest themselves in these two satellites.
I do not know what conclusion to take, what I noticed in this photo, for example, is that the spot is not uniform, it can be seen that the region near the Dendera crater (NASA right photo) is darker than the regions around it and This was also evident in the photo I took. In the right limbo at 3am there is the Osiris crater which is quite clear, and with a certain effort you can see that in my photo this region is also a bit clearer.
The truth is that at the moment I am working at the limits of resolution for the telescope and the camera that I have because of the seeing that I have had available, seeing this one, that, unlike what many may think, is far from being an Atacama.
In these conditions, anything recorded in something so small can be celebrated as a victory, and brings hope that on a night of really good seeing one can have a pleasant surprise!

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The detail certainly looks to be in the right place. Obviously these moons rotate, so we should see different  features everytime or do we always see the same side on these moons?

Edited by Pete Presland
missed the point I was trying to make
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Brilliant post and amazing image. I hope you are right but are you certain that at the time the image was taken was Ganymede orientated as shown? I believe the rotation is synchronous so i think this means that like our moon will always show the same face to Jupiter but not to anywhere else (I.e. us)

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