Audio
Fred Watson on Jupiter
Jupiter facts

Distance from sun778,000,000km (average)

Mass1.9 x 10^26kg, or 317.8 Earth masses

Number of moons16 classified moons, 12 unclassified satellites

Rotation period0.41 days

Planetary typeGas giant

Surface gravity22.88 m/sec^2 at equator

Cloud temperature-121°C

Like Earth, Jupiter is in orbit around the sun - but that’s where the similarities end! 

Named after the king of the Roman gods, our solar system’s largest planet is a gas giant more than 300 times the size of Earth – if it were hollow, more than 1000 Earths could fit inside it! It’s also got dozens of moons, and the storms that rage on Jupiter’s surface can not only be seen from here, one of them – the famous Great Red Spot (GRS)  – is three times as wide as the Earth!

Its size makes Jupiter a good viewing object in the night sky – it’s so bright it’s often mistaken for the ‘evening star’, Venus.

About Jupiter

The best known of Jupiter’s moons – Callisto, Europa, Ganymede and Io – were discovered by Galileo four centuries ago, and you can easily see these through binoculars.

If you’ve got access to a telescope, you can see the zones (light stripes) and bands (dark stripes) of Jupiter’s atmosphere. If you have a top-of-the-range telescope you may be able to make out the GRS, which moves across the face of Jupiter (transits) a couple of times each day. The stripes on Jupiter’s surface are the tops of giant jets of wind travelling in alternating directions at an incredible 650km/hr. The winds are probably powered by convection currents within the planet – Jupiter is still cooling down from its formation, and radiates about twice as much energy as it receives from the sun.

Jupiter also has a ring system like its neighbour Saturn, but you won’t see it. It’s only a tiny 10km deep and 6,500km wide – it wasn’t even discovered until Voyager 1 flew past the planet in 1979!

Did you know?

Jupiter’s atmosphere is 86 per cent hydrogen and 14 per cent helium, with traces of methane, water and ammonia – pretty much the ingredients that it takes to make a solar system. And while our planet is almost entirely molten rock, Jupiter is mostly liquid hydrogen.  The liquid is under such incredible pressure (4 million bars) that the hydrogen behaves as a metal, and conducts electricity – which could be what’s driving Jupiter’s massive magnetic field (20,000 times stronger than our own). Above the liquid hydrogen is a freezing layer of gas (-108 C), racked by storms bigger than the surface of our entire planet.  As you travel deep into the planet temperatures soar to an unimaginable 22,000C. It’s only here at the core of Jupiter that there’s the possibility of something Earth-like – a rocky lump, around 10 to 20 times the mass of our planet.

Where is Jupiter?

While the constellations are in fixed positions relative to one another, the planets roam across the sky from east to west in front of them. All planets follow the ecliptic, the path the sun takes across the sky.

The best time to see Jupiter (or any other planet) is when it is at opposition – when we are between it and the sun. At opposition planets rise at sunset and set at sunrise, giving us an entire night of viewing. The planets are closest to Earth during opposition so they look bigger at this time.
 

How to find Jupiter during National Science Week

Jupiter is at opposition in the Southern Hemisphere on August 15 – just in time for National Science Week! Having risen in the east at sunset, Jupiter will look like a bright star about 2.5 hand-spans above the eastern horizon from 7– 8pm. (Note: If you’ve got binoculars, you’ve got a good chance at seeing a Jovian moon or two – one or more moons pass in front of Jupiter on most nights during National Science Week).

Indigenous stories of Jupiter

Some Indigenous groups in Victoria believe Jupiter is Ginabongbearp, a chief of the Nurrumbunguttias, and husband of Chargee Gnowee, the sister of the sun (the planet Venus).  The  Pitjantjatjara/Aranda people in central Australia believe the planets Venus and Saturn are two brothers and Jupiter their dog.

Did you know?

One of the Galilean moons, Io, is the most volcanically active world in the entire solar system. It’s not so much what’s going on inside the planet - it’s just that Jupiter’s massive gravity is constantly tearing Io’s surface apart!