When you’re heading back from evening festivities this month, don’t be surprised to see a brilliant Christmas Star over in the east. In reality, it’s no star but the giant planet Jupiter, shining sensationally in the heavens.
Fittingly named for the King of the Gods in Roman mythology, Jupiter indeed lords it over the Solar System. Jupiter is so large that it could swallow 1,300 Earths: in fact, you could fit all the other planets inside its mighty bulk. That’s why it shines so brilliantly, even though the planet lies around 700 million kilometres from us.
Take a look at Jupiter through a pair of binoculars – holding them steady by resting your elbows on a wall or fence – and you can spot the planet’s four brightest moons (it boasts at least 67). They move around Jupiter from night to night, and it’s fun to watch their antics.
Grab a telescope, and you’re in for a treat. Jupiter’s reckless rate of spin (its day is less than 10 hours long) has flattened the planet into a tangerine-shape. And that same dizzy rotation has stretched its cream and ochre clouds of methane and ammonia into stripy bands.
The jewel in the planet’s crown has long been its Great Red Spot. Astronomers in the time of Charles II – using primitive telescopes – reported a dark spot in Jupiter’s clouds. It’s not clear whether the original spot has lasted for 350 years or if it faded away and a new spot erupted in the 19th century.
By late Victorian times, the spot was more like a giant rash. The livid red streak was three times the size of our planet Earth, and the Great Red Spot well merited its name. But time is healing the sore on the giant planet: the Great Red Spot hardly lives up to its billing any more. It’s now shrunk to little more than the size of the Earth; and its ruddy hue has faded to more subdued pink.
What’s going on? The spot is a great whirlpool in Jupiter’s clouds, feeding off the energy of the winds that zip past it. Perhaps the airstreams are changing and are no longer giving the Great Red Spot the energy it used to have.
The frothy clouds in the Great Red Spot tower high over the rest of the atmosphere and the colour seems to be fading as the clouds shrink downwards. That chimes in with a new theory for the spot’s colour.
Until recently, astronomers thought that reddish substances such as phosphorus or sulphur were bubbling up from deep inside the planet. But no chemical fits the colour perfectly.
According to the latest theory, though, the red colour is only skin-deep – right at the top of the Great Red Spot, where ammonia and acetylene in its towering clouds react together when they’re directly exposed to the Sun’s ultraviolet light. That means the Great Red Spot isn’t a deep-seated sore after all, but a case of high clouds suffering a local sunburn!
Apart from Jupiter, the planets aren’t putting on a great show this month. Look out for Venus in the second half of December, when it appears as an evening star low in the south-west about an hour after sunset.
Fainter Mercury is nearby; with binoculars, look to the lower right of Venus. Meanwhile, Mars makes its exit from the evening sky at around 7.30pm. Instead, this is the season when the stars are strutting their stuff.
The brilliant constellations of Orion, Taurus and Gemini are creating a glorious cosmic tableau in the south; Capella, the brightest star in Auriga, is climbing up the heavens to command the zenith for the next few months.
Shooting star fans should put their thermals on for the night of 13/14 December.
This is the peak of the Geminid meteor shower. The meteors come from an asteroid called Phaethon. It sheds rocky particles, which are quite chunky – and bright. In a dark environment, expect to see up to 100 slow-moving meteors per hour.
DIARY WHAT TO LOOK FOR
12.27pm full moon
Maximum of Geminid meteor shower
12.51pm moon at last quarter
11.03pm winter solstice: the shortest day
1.36am new moon
6.31pm moon at first quarter
Your month-by-month guide to the night sky next year: Stargazing 201 5 by Heather Couper and Nigel Henbest (Philip’s £6.99)Reuse content