SKY_September2014.pdf

52 September 2014 sky & tel-

escope

Jupiter’s Moons

3 EAST WEST

5

7

9

11

13

15

17

19

21

23

25

27

29

2

4

6

8

10

12

14

16

18

20

22

24

26

28

30

Oct 1

Europa

Ganymede

Io

Callisto

Sep 1

The wavy lines represent Jupiter’s four big satellites. The central

vertical band is Jupiter itself. Each gray or black horizontal band is

one day, from 0h (upper edge of band) to 24h UT (GMT). UT dates

are at left. Slide a paper’s edge down to your date and time, and

read across to see the satellites’ positions east or west of Jupiter.

In September you’ll fi nd Jupiter climb-

ing the eastern sky by the beginning of

dawn, shining in dim Cancer in the early

stage of its 13-month apparition across

the night sky from dawn to dusk.

As dawn brightens, the telescopic see-

ing often quiets down and high-power

views may become very sharp. Jupiter is

still on the far side of the Sun and nearly

as small as we ever see it, 32′′ to 33′′

across its fat equator. But it has been out

of good view since June. What have its

markings been doing in the meantime?

When we left off as Jupiter sank

toward the sunset, the North Equato-

rial Belt had become narrower and

slightly darker red-brown than the South

Equatorial Belt, as seen on this page.

The two great belts may be all that most

amateur telescopes show on Jupiter at the

beginning of this apparition. Have they

changed since you last looked?

Any telescope shows Jupiter’s four

large moons: Io, Europa, Ganymede,

and Callisto. Binoculars usually reveal at

least two or three, occasionally all four.

Identify them at any date and time in

September with the diagram at left.

Interactions between Jupiter and its

satellites are listed on the facing page.

Jupiter’s Great Red Spot is becoming

shorter and rounder with each passing

decade (July issue, page 16). This month

the Red Spot is a tough catch, with

Jupiter far away and not very high. A lot

will depend on how light or dark the spot

may have become. Here are the times,

in Universal Time, when it should cross

Jupiter’s central meridian. The dates,

also in UT, are in bold:

September 1, 5:32, 15:28; 2, 1:23, 11:19,

21:15; 3, 7:11, 17:06; 4, 3:02, 12:58, 22:54; 5,

8:50, 18:45; 6, 4:41, 14:37; 7, 0:33, 10:29,

20:24; 8, 6:20, 16:16; 9, 2:12, 12:07, 22:03;

10, 7:59, 17:55; 11, 3:51, 13:46, 23:42; 12,

9:38, 19:34; 13, 5:30, 15:25; 14, 1:21, 11:17,

21:13; 15, 7:08, 17:04; 16, 3:00, 12:56,

22:52; 17, 8:47, 18:43; 18, 4:39, 14:35; 19,

0:30, 10:26, 20:22; 20, 6:18, 16:13; 21,

2:09, 12:05, 22:01; 22, 7:57, 17:52; 23, 3:48,

The Return of Jupiter

13:44, 23:40; 24, 9:35, 19:31; 25, 5:27, 15:23;

26, 1:18, 11:14, 21:10; 27, 7:06, 17:01; 28,

2:57, 12:53, 22:49; 29, 8:44, 18:40; 30,

4:36, 14:32.

These times assume that the spot is

centered at System II longitude 223°. If

it’s not following predictions, it will tran-

sit 1^2 / 3 minutes early for every degree of

longitude less than 223°, or 1^2 / 3 minutes

later for e very degree greater than 223°.

Features on Jupiter appear closer to

the central meridian than to the limb for

50 minutes before and after transiting. A

light blue or green fi lter slightly boosts

the contrast of Jupiter’s reddish, orange,

and tan markings.

In these unusual scenes, which Chris-

topher Go took on May 20th eight

minutes apart, bright Io is smack in

front of the larger shadow of Gany-

mede. Ganymede itself is at left with

its disk resolved. South is up.

10:16 UT

10:24 UT

OBSERVING

Celestial Calendar

CC layout.indd 52 6/23/14 12:17 PM