In a previous post I explained that the biggest enemy of astronomers, next to odious public lighting, is the Earth's atmosphere. Last week the turbulences in our atmosphere (what we call "seeing") had settled down somewhat and I was able to make a better observation of the biggest planet of our solar system.
What struck me at first glace was the large number of dark wisps in Jupiter's bright equatorial belt. They do appear and disappear regularly in the planet's extremely stormy atmosphere but I can't recall to have seen so many of them at the same time.
Also interesting to note is Io, the third largest and innermost of the Galilean moons, which was transiting in front of the giant planet. Despite being larger than our Moon, in front of Jupiter it looks like a tiny, bright dot. Much more conspicuous was the shadow it cast on the planet and which you can see somewhat to the right. Remember that Io's pulled and squeezed so much by the gravitational interaction with Jupiter and its other moons that its entire surface moves constantly up and down one hundred metres! Compare that to the extremely mild tides on Earth! No wonder that Io displays the greatest volcanic activity of the entire Solar System.
A bit to the right lies the smallest of the Galilean moons: Europa. As I explained, this is perhaps the most interesting of Jupiter's moons because it hides a deep, liquid water ocean under its icy crust and there's strong evidence that it may even be suitable for life. Of course, Europa's too small and much too far away to be able to discern the many cracks and streaks on its constantly moving surface with amateur telescopes, but I did notice a darker patch near its left-hand border. For this reason I've created a highly magnified inset in the top-right corner, to show you my impression. In reality this moon was just the size of the dot on the main sketch of course.