Page 94 - BBC Sky at Night Beginners Guide to Astronomy - 2017 UK

THE PLANETS

PART 3 GAS GIANTS

BEYOND THE ORBIT OF MARS YOU’LL FIND SOME OF THE MOST
EXCITING AND HOSTILE ENVIRONMENTS IN THE SOLAR SYSTEM.
HERE WE TAKE A LOOK AT JUPITER AND THE PLANETS BEYOND

Following the small planetary the outer worlds. From Jupiter Sun. This can be observed from lifetime of 75 years, it won’t have
hops within the warm inner onwards not only is it colder, their tiny weekly movements completed even half a Neptunian
Solar System in part two, we but the planets also travel at an across the sky. Neptune, for year – it will still have the other
now take a trip across the vast increasingly slow pace owing to example, travels so slowly half of its journey around the
stretches of colder space to less gravitational pull from the that, during an average human Sun to go.

JUPITER Jupiter is a fi ne observing target.
With a good pair of binoculars
the fi rst things you’ll notice are
Mean distance from the Sun: its main moons: Io, Europa,
778 million km Ganymede and Callisto. With
Rotation period: 9 hrs 55 min a telescope you’ll see a slightly
Orbital period: 11.9 years squashed sphere. This is due to its
Diameter: 142,800km fast spinning ‘day’ of just under 10
Gravity (Earth=1): 2.69 hours, which causes the equator to
Mean atmospheric temperature: –153˚C bulge outwards and the poles to
Number of moons: 63
fl atten. Jupiter’s cloudy atmosphere
will be revealed as dark bands
separated by white zones. The
longer you look, the more features
appear, so keep an eye out for
spots, wisps and kinks. The most
famous feature is, of course, the
Great Red Spot, a storm that
changes shape, size and colour
over time, often appearing
quite greyish.
At around the time of opposition
– when the planet is opposite to
NASA/JPL X 4, STEVE MARSH X 2, JOHN CHUMACK/SCIENCE PHOTO LIBRARY X 2
the Sun in the sky and closest to
Earth – Jupiter becomes a sparkly
night-time beacon. Shining at a
maximum magnitude of –2.8,
it appears as an unmistakable
‘star’ that will certainly catch your
attention. The next few opposition
dates for Jupiter are 3 December
2012, 6 January 2014 and 7
February 2015. These are the best
times to see the planet shine.Being
closer to Earth means Jupiter is at
its largest appearance-wise – great
for anyone who owns binoculars
Jupiter’s distinctive
Great Red Spot and or a telescope. Don’t expect to
bands are clearly see all of its big satellites though,
visible through a small as they could be in front of, or
telescope, inset behind, the planet.

94 skyatnightmagazine.com 2012