Jupiter

Jupiter is the largest planet in the solar system, the 5th from the Sun. It is not quite as bright as Venus when seen from Earth.

Measured across, Jupiter is ten times the size of the Earth and one-tenth the size of the Sun. Like the Sun and Saturn, it is mostly hydrogen and helium. There may be a small core of rock and perhaps ice at the center. This is surrounded by an ocean of liquid hydrogen and helium in the form of a metal. Above this is a layer of liquid hydrogen and helium, and above this a thick atmosphere.

Image of Jupiter from NASA, ESA, and E. Karkoschka (University of Arizona)

Jupiter is radiating energy, possibly as a result of radioactivity. The most famous feature is the Great Red Spot, which may be a huge storm in the atmosphere. If so it must be quite a storm, as it has been recorded for 300 years!

Jupiter also has a faint ring made of dust which was only recently discovered.

Far more easy to see are the moons. The four largest of these were seen by Galileo when he made one of the first telescopes. The way they moved round the planet convinced him that the old idea, that everything moves round the Earth, must be wrong.