Jupiter – King of Planets

The planet Jupiter has been known since ancient times. It is visible to the naked eye in the night sky and can occasionally be seen in the daytime when the Sun is low. To the Babylonians, this planet represented their god Marduk. The Romans named the planet after Jupiter, the principal god of Roman mythology. The Greek equivalent of the Roman Jupiter was Zeus.

Jupiter is the fifth planet from the Sun and the largest in the Solar System. It is a giant planet with a mass two and a half times that of all the other planets in the Solar System combined. Jupiter can be bright enough for its light to cast shadows, making it the third-brightest object in the night sky after the Moon and Venus.

Through modern binoculars you should be able to see what Galileo spotted with his first telescope in the 17th century. The planet appears as a disc and if you hold your binoculars steady enough you should be able to see the four Galilean moons orbiting the planet.

This discovery was dynamite in the 17th century. In those days people believed that everything in God’s perfect universe rotated around the earth. But Galileo had spotted moons going round Jupiter. This was one of the observations that persuaded him to support the Copernican theory that the planets orbited the sun rather than the earth. Eventually Galileo was convicted of heresy for these views. Forced to recant by the Inquisition he spent the rest of his life under house arrest.

More can be seen through a modest telescope. At even a low magnification of x50, two dark bands of clouds can be seen circling the middle of the planet. If you are lucky you may even catch a glimpse of the great red spot, a giant storm that is known to have existed since at least the 17th century.

Jupiter with Europa’s shadow and the great red spot
The Galilean Moons

Jupiter has 67 known moons. The four largest were discovered by Galileo. These moons were named after lovers of the god Zeus: Io, Europa, Ganymede and Callisto.

Io was one of Hera’s priestesses

Io is the closest moon to Jupiter and orbits the planet in less than two earth days. This proximity sets up huge tidal stresses in Io’s surface which heat the rocks and melts them. As a result Io is the most geologically active object in the solar system, with over 400 live volcanoes.

Europa was a mythical Phoenician noblewoman, who became queen of Crete

The second Galilean moon, Europa, is one of the smoothest objects in the solar system. The surface is made of ice and it is thought that an ocean of liquid water exists underneath the ice. Like Io, it is heated by tidal flexing in Jupiter’s immense gravitational field. Some scientists think that extra-terrestrial life could exist in Europa’s ocean.

Ganymede was the cup bearer of the Greek gods

Ganymede is the third Galilean moon. It is bigger than the planet Mercury and is the largest natural satellite in the solar system. This moon is primarily composed of rock and water ice. There may be an ocean at a depth of 200km, sandwiched between layers of ice.

Callisto was a hunting companion of the goddess Artemis

Callisto, the fourth Galilean moon, is one of the most heavily cratered satellites in the solar system. It has long been considered the most suitable base for future exploration of the Jovian system because it is the furthest large moon from Jupiter’s intense radiation.

Of course not even the Hubble space telescope can take pictures like the ones above. You need to get close up for images like that! The picture of Jupiter is from NASA’s Cassini mission and the moon’s are from their Galileo mission.