Australian Sky & Telescope - May 2018

56 AUSTRALIAN SKY & TELESCOPE May | June 2018

JUPITER’S 2018 OPPOSITION by by S. N. Johnson-Roehr

Jupiter’s time

to shine

The Solar System’s greatest gas giant will

put on a bold appearance as it reaches

opposition in May.

SThis colour-enhanced image, taken as the spacecraft Juno lew

by Jupiter on December 16, 2017, shows the intense storm patterns

in the cloud bands of Jupiter’s northern hemisphere. NASA / JPL-CALTECH / SWRI / MSSS / BJÖRN JÓNSSON

J

upiter spent autumn creeping through the night.

Just a few months ago, an audience with the Solar

System’s ‘monarch’ was an early morning pleasure,

best taken care of before beginning the work day. Now,

Jupiter appears with the dark, its rise coinciding with the

setting of the Sun on May 9, the date of opposition. Jupiter

rises about 30 minutes after sunset on the first evening of

May and sets about two hours before the first sunrise of June,

which means Jove is up the entire night during May, for all

practical purposes. Even more important for visual observers:

Jupiter is highest, and thus in the steadiest part of the sky,

in the middle of the night. It transits about 45 minutes after

midnight on May 1 and 70 minutes before midnight on the

31st. Altitude is essential for the best view of this gas giant;

when Jupiter is up high, out of the haze above the horizon,

you’ll have the best shot at steady seeing (i.e. looking through

less atmospheric turbulence).

Observing the giant

Even in the steadiest part of the sky, good observations of

planets happen a millisecond at a time. Improve your views

by setting up your optics early in the evening to let them

adjust to the ambient temperature. Then, when Jupiter rides

high in the sky, focus on the planet’s edge and settle in for

a good, long study session. The moments of absolute clarity

are fleeting, and you’ll find yourself instinctively testing your

focus every now and again. It’s good to check every once in a

while, but patience is really your best tool here.

Once you’ve found the planet and tested your focusing

skills, increase the magnification. You’ll find Jupiter goes a

bit blurry pretty quickly. With my 12.5-cm, f/5 reflector, I

stop trying for more by the time I hit 150×. The 25-cm f/4.5

reflector shows Jupiter at its best around 250× or so, though

occasionally a bit more power is better. It’s tricky to find the

perfect balance of magnification and sharpness, but that’s

part of the observing fun.

If you’re having difficulty distinguishing Jupiter’s

atmospheric features, add a filter to your setup. Over the

years, I’ve found a #80A (blue) filter to be the most useful for

‘bumping’ the contrast of the cloud bands, but #38A (dark

blue) and #82A (light blue) may be better for you — try them

all if you have them. Many observers find #8, #11, and #12

(yellow and yellow-green) filters help draw out details in the

belts and polar regions. I sometimes screw on a #25 (red)

filter for kicks and contrast, but usually return to a blue filter

after a few minutes.

One of the great things about Jupiter is that our view of it

changes relatively quickly. One Jovian revolution takes just

under 10 Earth hours, so if you observe early, then return

to the planet later that night, you’ll see a decidedly different

picture. The diagram at the right shows Jupiter’s main

markings. Through a small scope, you should be able to see

the two major cloud bands, the South and North Equatorial

Belts. From there, it’s a matter of spotting subtleties. Jupiter’s