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					Observing Jupiter

The king
                                                                               Above: Jupiter presents a wealth of detail in
                                                                               amateur telescopes. Image Damian Peach

                        of the planets
Although this year may not be a standout year for Jupiter, Damian Peach
shows that it still keeps its crown as king of the planets.

                                                                                       uring the cold January mornings          nightly motions of the four Galilean moons
                                                                                       many observers out during the early      (Io, Europa, Ganymede and Callisto) as four
                                                                                       hours will note the giant planet         bright points close to the small Jovian disc.
                                                                             Jupiter again returns to our skies. Despite             Using a good 15cm (6-inch) reflector
                                                                             not being in a great position for Northern         or 10cm (4-inch) refractor will reveal all the
                                                                             Hemisphere observers when it reaches               major dark belts and bright zones, as well
                                                                             opposition on 6 June 2007, Jupiter will still      as features such as the Great Red Spot and
                                                                             present a large disc, so even though it will       wispy festoons projecting from the dark
                                                                             not be high in the sky, plenty can still be seen   North Equatorial Belt (NEB). Those with
                                                                             and imaged through amateur telescopes.             larger telescopes in the 20cm plus range
                                                                             At opposition, Jupiter will be placed in the       Jupiter reveals a wealth of fine detail under
                                                                             southern constellation of Scorpius, only           good conditions. Jupiter shows a great range
                                                                             seven degrees from the deep red star Antares       of features and the terminology takes some
                                                                             and the two will make a prominent pairing          to become familiar with. The two major
                                                                             throughout the year.                               belts of the planet are the NEB and the
                                                                                  Jupiter’s observable atmosphere is            South Equatorial Belt (SEB.) All the major
                                                                             structured in alternating dark belts and           belts and zones are displayed in the diagram.
                                                                             bright zones. The actual boundaries of                  Jupiter’s rotation period (unlike that of
                                                                             the belts and zones aren’t defined by               Earth) is divided into three systems due to
                                                                             their appearance, but by their latitudinal         the clouds in the equatorial regions moving
                                                                             boundaries, delineated by the fast moving          faster than the clouds farther north or south.
                                                                             atmospheric jet streams that keep everything       They are called System 1 (the equatorial
                                                                             ‘in check’.                                        regions as far north as, and including,
                                                                                  A question many beginners ask is              the NEB’s southern edge and the SEB’s
                                                                             “what can I see on Jupiter?” The answer is,        northern edge), System 2 (the rest of the
                                                                             generally a great deal with patience. With         planet down to the NEB’s southern edge
                                                                             a good pair of binoculars (10 x 50s are a          and SEB’s northern edge) and System 3,
                                                                             good choice) you will be able to follow the        which refers to the rotation period of Jupiter

Above: Jupiter’s largest moons, the Galilean
moons, can be followed as they orbit the
giant planet. The top graphic presents a mock
photographic view of the scene on 24 May, with
Jupiter overexposed from a long exposure to
bring out the moons as they line up to the left    Right: Jupiter is ringed with belts,
of Jupiter. The centre graphic shows the view      each labelled here in this image, which has
through binoculars on the 3 June, with the         south to the top, matching the view seen
moons now all lined up on the opposite side.       through some telescopes that invert north and
Finally, the last graphic simulates a telescopic   south. Key: SPR: South Polar Region; STB: South
view on 12 June when Io just completes             Temperate Belt; SEB: South Equatorial Belt; EZ:
its transit of Jupiter, while Ganymede just        Equatorial Zone; NEB: North Equatorial Belt;
reappears from behind the planet’s limb on the     NTB: North Temperate Belt; NPR: North Polar
other side. In all instances north is up.          Region. Image: Damian Peach.
AN graphics by Greg Smye–Rumsby.                   Additional graphic design: Greg Smye–Rumsby.

84    Astronomy Now Yearbook 2007
                                                                                                                                                              Observing Jupiter

observed at radio wavelengths, and thought          of the UK often suffer from poor seeing             THE USE OF COLOURED FILTERS.
to be the rotation period of the planet’s core.     conditions, which make obtaining that
     The major limitation the observer              good image difficult. Once the basics of the         One great observing aid not just for Jupiter, but all the
will find (given his telescope is of good            observer’s telescope have been mastered
                                                                                                        planets, is the use of coloured filters (which screw into
quality and he/she has the telescope in good        (collimation, focusing, tracking) they will
                                                                                                        the bottom of the eyepiece or camera). These can give
collimation) is atmospheric seeing. The             be ready to undertake a night of imaging.
                                                                                                        much clearer views of surface/atmospheric details
lower an object is in the sky, the more of          I can’t stress enough the importance of
                                                                                                        and also aid in estimates of the intensities of various
Earth’s atmosphere its light passes through         properly collimating the telescope. The
                                                                                                        features. For Jupiter the most useful filters to aid the
before it reaches the observer. Since Jupiter       observer should check the collimation
will appear low in the sky in 2007, the use of      before observing or imaging and make
                                                                                                        visual observer are red and blue. Smaller scopes (less
coloured filters to observe and image it will        the adjustments if needed. Also once the            than 20cm aperture) may prefer orange or light blue.
yield much clearer views than without filters.       CCD camera/webcam has been attached,                For example I prefer using orange to red even on my
     Red filters will help enhance the               don’t rush focusing. Take as much time as           36cm reflector. Filters worth considering are Wratten
blue coloured areas of Jupiter. They also           is needed to reach perfect focus. With the          #25 (red), #21 (orange), #38A (dark blue) and #80A
penetrate the violet absorbing haze that            planet low in the sky it is essential to use        (light blue).
hangs over Jupiter’s atmosphere, so will            an infrared blocking filter, especially when
penetrate deeper into the atmosphere. Red           imaging with colour cameras such as the
or orange filtered views tend to be by far           Philips T  oUcam.
the most detailed and I highly recommend                 Tri-colour CCD imaging is the
them, especially with Jupiter being so low in       most challenging area but yields the best
the sky. Blue filters will enhance the redder        possible results. One must obtain a red,
coloured areas of the atmosphere and the            green and blue filtered image in under
belts will appear very dark through this filter.     approximately two minutes because of
The Great Red Spot also appears much                Jupiter’s fast rotation.                            Jupiter displays different details through different coloured filters
darker in blue coloured filters. Observers                One area worth special mention                 as shown in these images. A blue filter was used for the image on
using CCD cameras can also employ a wide            during the 2007 apparition is the use of            the left, a green filter for the centre image and a red filter for the
                                                                                                        picture on the right. Image: Damian Peach.
range of filters (see The use of coloured filters).
                                          lters     infrared pass filters for imaging. Seeing
     A great way to learn more about Jupiter        conditions are much less turbulent in the
and become familiar with its features its           far-red wavelengths and images taken
to draw the planet. For centuries this was          through filters that pass light from 700
the only way to record Jovian activity and          nanometres and up will produce the best
remains to this day an ideal way to ‘learn          results possible with the planet so low in
the ropes’ of observing the giant planet.           the sky. These filters are not expensive
More detail and advice on visual observing          and it’s well worth investing in one for
is available from organisations such as the         the coming Jupiter apparition.
British Astronomical Association (www.                   Once the observer has obtained
britastro.org.)                                     the raw images, they can proceed to
                                                    processing them on the computer.
CCD and webcam imaging                              Unsharp masking is by far the most
As well as being a fascinating target for the       common routine used for sharpening
visual observer, Jupiter is an excellent target     images, and works very well. One should
for today’s amateur equipped with a CCD             be careful not to over-sharpen their
camera or webcam.                                   images, but process them so as much
     CCD imaging of Jupiter in the last few         detail as possible is displayed, with as little
years has revolutionised amateur study of           visible noise as possible. Programs such
the planet. Experienced amateurs today              as Registax are commonly used to process
are regularly producing CCD images with             webcam sequences and this is available            Above: Jupiter (upper left) will be six degrees north of the Moon, with
20cm (8-inch) to 40cm (16-inch) telescopes          for free download at http://registax.             bright red star Antares just 0.5 degrees north, on 28 June. Jupiter and
                                                                                                      Antares, twin red objects, will be close together for much of the summer.
that exceed the quality and resolution of           astronomy.net/                                    AN graphic by Greg Smye–Rumsby.
photographs produced from professional
mountaintop observatories 20 years ago.             Further advice and information
The very best images produced can resolve           Observers should consider sending there
low contrast features down to around 0.2            visual drawings and CCD images to the
arcseconds, giving such images an almost            British Astronomical Association. Observers         JUPITER FACT FILE
‘Hubble-esque’ appearance.                          can find information on the Jupiter section’s
     CCDs today have never been more                activities on their web page. Books such as         Equatorial diameter:                                     143,082km
affordable. Equipped with a good 15cm               The Giant Planet Jupiter by John Rogers             Polar diameter:                                          133,792km
telescope, webcam and PC, observers can             provide a wealth of information about
produce detailed nightly images of Jupiter          Jupiter, while The Lunar and Planetary              Rotation period of System I:                             9h 50m 30s
that are not only fascinating to look at but        Webcam User Guide by Martin Mobberley               Rotation period of System II:                            9h 55m 40s
scientifically valuable as well. Webcams such        would be an excellent choice to learn more          Rotation period of System III:                           9h 55m 30s
as the Phillips T  oUcam, which costs around        about the vast subject of CCD imaging of
£50, has brought high-resolution imaging            the planets.                                        Mass:                                      1.9 x 1027kg
into an affordable price bracket and the                 For me, Jupiter is without doubt the                  (as much as all the other planets put together!)
keen amateur could equip themselves with            planetary jewel of the sky. Large, bright and       Mean albedo:                                       0.52
a system that could produce detailed images         always changing in an appearance it can             Mean distance from Sun:                 730 million km
for as little as £500.                              provide many hours of viewing pleasure for          Mean distance from Earth:               581 million km
     Obtaining good images will take a              observers using a wide range of astronomical        Angular diameter:                    31–49 arcseconds
lot of practice and patience. Most areas            instruments.

                                                                                                                                          Astronomy Now Yearbook 2007            85