Comments: 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!

[Add observation]

Observation 1
Feature(s)	N/A
Filter(s)	l astronomik
Date	2017-04-30 02:25:44
Julian day	2457873.6006944445
System I	26.75°
System II	315.97°
System III	81.0°
Illumination	100.0%
Phase angle	4.400000095367432°
Solar longitude	279.4°
Eq. diameter	1.6″
Derotation	0.0 min