Destination Jupiter: Observing the Mighty Giant
Jupiter's Great Red Spot as seen by the Voyager 1 probe in 1979.NASA
The Autumn and Winter months of 2012 are an ideal time to observe the mighty planet Jupiter.
Over the years, we've seen some fantastic photographs from the Voyager probes (1979) and Galileo orbiter (1995-2003), even the Earth-orbiting Hubble Space Telescope has captured some crisp images of the gas giant. Flybys by recent spacecraft — the Saturn-bound Cassini and Pluto-bound New Horizons — also provided excellent, if fleeting, glances of this massive world.
But it isn't just the big professional telescopes that reveal stunning detail on this giant neighbour of ours. Armed with even a modest telescope and good, stable, clear skies there's a surprising amount of detail accessible to the amateur astronomer.
Starting with the practicalities, the planet itself is easily visible to the naked eye and during the coming months can be seen around the stars of Taurus. Find the distinctive 'V' shape of the Hyades cluster marking the head of the bull and Jupiter is the bright 'star' just to the west.
Pointing a pair of 7x50 binoculars at Jupiter and holding them steady will just reveal four of its satellites; Io, Europa, Ganymede and Callisto. They can be seen in a straight line extending from either side of the planet. Watch them over a few hours and nights to see how they change position. On occasion some will seem to disappear due to passing in front or behind Jupiter.
A telescope that provides magnification of 40 or more will start to show detail on the planet itself. Jupiter is a large gas giant, meaning telescopic views show the top of the gas layer. Magnified views reveal detail in the atmosphere such as the famous belts running around the planet. The belts are the result of high velocity winds running in opposing directions at different latitudes. This has the result of producing the characteristic belts of differing color relating to the different gasses confined in that area.
The two most prominent belts are the northern and southern equatorial belts that run either side of the equator. They have a distinct brown color through even the smallest telescope and stand out in contrast to the pale background of the planet. The planet rotates once on its axis in about 10 hours, meaning any feature can move quite quickly out of view from Earth. A good example of such a feature is the Great Red Spot, which is a large hurricane system about 3 times the size of Earth. It can be seen as a pale red/brown spot embedded in the southern edge of the south equatorial belt.
Despite these obvious features, there are many more belts that can be seen but its dependent on size and quality of the telescope, the weather conditions and, to a lesser extent, the experience of the observer.
To get the best out of any planetary observation, don't use a ridiculously high magnification — start low and change the eyepiece to slowly increase magnification. If the weather is good then you will be able to use a higher magnification but a turbulent unsettled air mass will make the image jump around, be quite disappointing and render high magnifications pointless. Take your time at the eyepiece and wait for those moments where the atmosphere becomes briefly stable for just a short time — its in those moments that the best views will be seen, and it's also when Jupiter will take your breath away.