Dazzling sight of Jupiter and its many moons

On 8 March, Jupiter is at its closest to the Earth, and is the most brilliant “star” in the heavens all night long. You can’t miss it – the planet lies in the south below the constellation Leo, and shines with a steady, yellowish glow.

Of course, as in anything astronomical, close is a relative word. Jupiter lies 700 million kilometres away, but its giant bulk – it measures 143,000km across – means that it reflects sunlight sensationally and, as a result, the planet is a dazzling sight in our night skies.

Jupiter is the giant of our Solar System; it could swallow 1,300 Earths. And as befits its mighty status, it is home to a family of almost 70 moons. The biggest four are hugely entertaining to watch, circling their planet in a matter of days. They are a great sight through powerful binoculars or a small telescope. One 78-yearold lady at an evening course we held could even see them with the unaided eye!

These are worlds in their own right, with very different personalities. Ganymede, the largest, is bigger than the planet Mercury. It has an icy crust peppered with impact craters caused by meteorite bombardment in the early years of the Solar System. But the moon has evidently been more active recently: it is riddled with ridges and grooves, testifying to geological activity.

Callisto is similarly cratered. Its icy surface shows the mark of a huge impact: the crater Valhalla – 300km across.

And now for something completely different. Io, yellow-orange, looks like a cosmic pizza. Instead of being a rather dead moon covered in craters, like Callisto, it’s a hotbed of activity. Volcanoes shoot plumes of sulphur dioxide 300km into space. This is the most violent world in our Solar System. The driver appears to be Jupiter’s vast gravity, which pummels the interior of this hapless moon and stirs up the fireworks.

Then we come to Europa. Pure white, icy, and smoother than a billiard ball, this is the moon that is keeping scientists intrigued. They believe that – below its thick, icy crust – Europa may be concealing a deep ocean of water. A possible abode for aquatic life?

But back to the giant planet itself. Jupiter’s Great Red Spot – a storm that has been raging for centuries – is not what it used to be. A con- stant feature of the planet for at least 250 years – and once three times the width of the Earth – it is shrinking and growing paler.

No one knows why this cyclone-like structure is behaving like this. However, we may have an answer soon. In July, Nasa’s Juno space probe will go into orbit about Jupiter. It will probe the atmosphere and interior of the huge, gaseous world – and reveal things we have never known before about the undoubted king of our planetary system.

WHAT’S UP

The night belongs to Jupiter (see above). But drag your eyes away from the spectacular planet and you can take in a great display of stars. In March, we are treated to more brilliant stars than in any other month of the year.

Over in the west, seek out the familiar humanoid shape of Orion, emblazoned with red Betelgeuse and blue-white Rigel. Nearby are the two dog stars, Sirius and Procyon, and reddish Aldebaran marking the eye of Taurus, the bull. Higher up you’ll find the twin stars of Gemini – Castor and Pollux – and Capella, the little she-goat.

The star to the right of Jupiter is Regulus, the heart of Leo, the lion. To its left you’ll find Spica (in Virgo) and Arcturus. Finally, low in the north-east, Vega and Deneb are patiently waiting their turn to rise higher over the next few months, and dominate the summer skies.

After midnight, they are joined by two more planets: Mars, rising in the south-east, and, an hour later, by Saturn. Finally, we can say that winter is definitely over: the Spring Equinox falls on 20 March, and British Summer Time begins on Easter Day, 27 March.