Australian Sky & Telescope - May 2018

http://www.skyandtelescope.com.au 57

GANYMEDE: DAMIAN PEACH / CHILESCOPE TEAM; JUPITER DIAGRAM: GREG

G DINDERMAN /

S&T

belts, both equatorial and temperate, are slightly

ruddy or beige through the eyepiece. They’re

separated by brighter, whiter bands called zones.

Distinguishing white-ish zones from wheat-ish

belts is a full night’s work.

Within the zones and belts rage storms. Look

for these ovals, tight gatherings of clouds that

dot Jupiter’s bands. White ovals, which often

develop in the South Temperate Belt, can really

‘pop’ through the eyepiece. Ovals can also be

red, as in the Great Red Spot, or grey. Barges

resemble compressed ovals; they’re dark and red,

but somewhat linear or blocky. Study the belts for

variations in colour caused by rifts, long, bright

streaks that stretch along the darker bands.

Readily apparent in images but more elusive to the eye are

festoons, tendril-like blue-grey features that angle into zones

from a belt.

TheGreatRedSpot

Ifyoutimeyourobservingtocoincidewiththetransitof

theGreatRedSpot(GRS),thechangesontheplanet’sface

become even more obvious. The GRS, which sits in a pocket

betweentheSouthEquatorialBeltandtheSouthTropical

Zonecalled‘RedSpotHollow,’canbeachallengeforobservers

with small scopes. Your best chance at seeing it is within an

hourofthetimeitcrossestheplanet’scentralmeridian.Here

are those crossing times, in Universal Time, as predicted for

lateAprilandMay.Thedates,alsoinUT,areinbold.

April 15,1:41, 11:37, 21:32;16,7:28, 17:24;17,3:19,

13:15, 23:10;18,9:06, 19:01;19,4:57, 14:53;20,0:48, 10:44,

20:39;21,6:35, 16:31;22,2:26, 12:22, 22:17;23,8:13, 18:08;

24,4:04, 14:00, 23:55;25,9:51, 19:46;26,5:42, 15:37;27,

1:33, 11:29, 21:24;28,7:20, 17:15;29,3:11, 13:07, 23:02;30,

8:58, 18:53.

May 1,4:49, 14:44;2,0:40, 10:36, 20:31;3,6:27, 16:22;4,

2:18, 12:14, 22:09;5,8:05, 8:00;6,3:56, 13:51, 23:47;7,9:43,

19:38;8,5:34, 15:29;9,1:25, 11:21, 21:16;10,7:12, 17:07;

11 , 3:03, 12:59, 22:54;12,8:50, 18:45;13,4:41, 14:37;14,

0:32, 10:28, 20:23;15,6:19, 16:14;16,2:10, 12:06, 22:01;17,

7:57, 17:52;18,3:48, 13:44, 23:39;19,9:35, 19:30;20,5:26,

15:22;21,1:17, 11:13, 21:08;22,7:04, 17:0 0;23,2:55, 12:51,

22:47;24,8:42, 18:38;25,4:33, 14:29;26,0:25, 10:20, 20:16;

27,6:11, 16:07;28,2:03,11:58,21:54;29,7:50, 17:45;30,

3:41, 13:36, 23:32;31,9:28, 19:23.

ThesetimesassumethatthespotwillbecentredatSystem

IIlongitude288°.IftheRedSpothasmoved,itwilltransit

12 / 3 minutesearlierforeachdegreelessthan288°and1^2 / 3

minutes later for each degree more than 288°.

Jupiter’s moons

With Jupiter at opposition the planet is at its boldest and

brightest for the year, and so too are its Galilean moons.

With close observing and the right equipment, you can detect

differences in their sizes and colours (Io gives itself away with

its orange-yellow appearance, Ganymede is the largest of the

four). At opposition, Europa will appear the smallest, with

a diameter of 1.0′′. Io will show at 1.1′′, Callisto at 1.5′′, and

Ganymede will boast a whopping 1.7′′ diameter. Yes, these are

tiny differences, but after enough repeat visits to the quartet,

you’ll be able to distinguish them from one another with ease.

Take the time to make a sketch, keeping in mind that a

polished drawing isn’t necessarily the goal. Rather, it’s the

process of looking while you’re recording the view that will

help you learn the planet. Don’t worry about your cramped

handwriting or inability to replicate the subtle bands of

Jupiter’s globe on the page. Even a ‘sketch in prose’ can be

useful: What colour are the belts? Can you see any texture in

them? Did you see the Great Red Spot? How were the planet’s

satellites positioned? Anything that helps you remember those

brilliant moments of perfect seeing is good enough to put on

paper. My best advice: If you think it, write it down, because

you’re unlikely to remember that thought or impression after

a short night’s sleep.

S. Tropical Zone

Equatorial Zone

N. Tropical Zone

N. Temperate Zone

Central meridian (CM)

Direction of

rotation

Great Red Spot

S. Equatorial Belt

N. Equatorial Belt

Equatorial Band

SOUTH

NORTH

S. Temperate Zone

South Polar Region

North Polar Region

Belts (dark)

Zones (bright) S. S. Temperate Belt

S. Temperate Belt

N. Temperate Belt

N. N. Temperate Belt

SThe features of Jupiter change in intensity, size and position over

time; this basic schema should help you identify what you see through

your eyepiece. South is up to match the view in many telescopes.

Features rotate from celestial east to west.

Using a 1-metre

Ritchey-Chrétien

telescope, Damian

Peach captured the

shadow of Ganymede

(top left) as it travelled

across the face of

Jupiter in March 2017.

Golden Io gleams to

the right of the planet.