Seeing Jupiter through a telescope for the first time is an experience never to be forgotten. That bright point of light that gleams down from the sky above resolves, as if by magic, into a gloriously large disc of light. Dark belts and brighter zones smear across the view. No need to adjust your telescope’s eyepiece! What you’re seeing is Jupiter for real – its turbulent atmosphere in full dynamic motion.
But viewing Jupiter through a telescope is not just about a momentary glance. Let your eye linger longer at your telescope’s eyepiece. When you do you’ll start to pick out subtle details – rifts in the dark bands; dark spots rolling out over the chaotic upper cloudscape, and thinner bands that break and reform across the disc. It’s a maze of ambiguous lines and swirls so reminiscent of a science experiment involving coloured fluids mixing together in mesmerizing patterns.
In fact what you’re seeing on Jupiter through a telescope is this type of ‘experiment’ played out on a massive scale. The zonal appearance of Jupiter’s surface is a gaseous mix of chemical clouds driven along by high velocity winds in Jupiter’s upper atmosphere. The darker bands equate to warmer lower zones in the atmosphere, while the lighter zones are colder higher cloud levels composed of ammonia crystals.
At the boundary of each belt and zone is extreme wind shear – a potent force in the creation of swirling storms like the Great Red Spot (GRS).
The Great Red Spot
More than twice as large as the Earth, Jupiter’s GRS is the largest storm system known. It is also the oldest. Astronomers think that the storm has persisted for more than 300 years.
A small telescope will easily show the Great Red Spot on Jupiter. But you have to know when to look. Jupiter rotates once every 9 hours and 55 minutes. You’ll therefore only have a couple of hours’ opportunity to view the famous storm on each rotation. If that happens to be in daylight or at a time when Jupiter isn’t above the horizon then you won’t get to see it.
Thankfully, as we head into autumn 2012 Jupiter rises earlier and earlier so there’s plenty of opportunity to see the GRS. At the beginning of September the king of the solar system is up above the local horizon for mid northern latitudes by midnight, making it easily observable with a telescope by 1.30am. Come the start of October Jupiter is rising by 9.30pm local time, and observable through a telescope by about 11pm.
Why am I stating a difference between rise time and observable time through a telescope? The simple answer is atmospheric turbulence.
When you look at an object in the night sky when it’s low down on the horizon you’re actually looking at it through a thick slice of Earth’s atmosphere. This dims the view, and being low down to the horizon your view can suffer a lot from turbulent air currents.
Waiting 1-2 hours after Jupiter has risen to view it through a telescope will give it enough time to rise higher into the sky. The further you are away from the horizon the smaller the slice of Earth’s atmosphere that you’re looking through, and so the steadier and clearer your view should be.
It’s all in the detail
If you don’t already own a telescope, the best way to see Jupiter is to go to an observing evening run by your local astronomy society this autumn, or hire a telescope to view it yourself.
If you opt to hire a telescope an 8″ dobsonian telescope will work well. It’s a manageable size for a beginner and portable enough to be carried to a good location in your garden, backyard or other observing spot. With an 8″ dobsonian telescope the mirror is large enough to collect a good amount of light to start revealing some of the more intricate details in Jupiter’s cloud belts.
Make sure your hire telescope comes with a medium or high power eyepiece combination too. A quality eyepiece in the 10mm to 5mm range will give you high enough magnification to yield a good amount of detail.
Jupiter will be visible in our late evening skies throughout the autumn. By the time winter rolls around Jupiter will be rising shortly after sunset, making it a spectacular object to follow with a telescope all night.