The planet is a giant ball of gas and liquid around 500 million miles from the Sun. It's surface is composed of dense red, brown, yellow, and white clouds arranged in light-coloured areas called zones and darker regions called belts.One of the puzzling aspects of this enormous gas planet is that it loses or gains a large stripe about once every 15 years. No one knows why. Also, no one knows for sure why the famed Great Red Spot, a hurricane like swirl of gas in the southern hemisphere, has remained stable for centuries.
These clouds are created by chemicals that have formed at different heights. The highest white clouds in the zones are made of crystals of frozen ammonia. Darker, lower clouds are created from chemicals including sulphur and phosphorus. The clouds are blown into bands by 350 mph winds caused by Jupiter's rapid rotation.
Though, it does appear to be shrinking. It is about the width of three Earths side by side, but has shrunk by about 15% from 1996-2006. And, scientists are not even sure why it is red. The shape has changed over the past couple of centuries, however. It used to be much more 'squashed', i.e. sausage shaped, rather than eye-like. By "stable" I just mean that, despite the huge winds blowing it around through other gases, it doesn't disappear and reappear.
Planetary astrophysics was never my bag but I confess that sometimes it's very easy to see why a few get hooked on it. Even though the phenomena are ultimately explained by Newtonian fluid mechanics, it shows that — even without the weirdness of Quantum Mechanics or the counter-intuitive effects of Relativity — we still have much to learn about 'ordinary' things.