Sky & Telescope - January 2021 - 51
Action at Jupiter
THE JUPITER OBSERVING SEASON
is ending. At the start of January the
planet is low in the southwest and
sets 1h 45m after the Sun. On January
1st, Jupiter shines brightly at magnitude -2.0 and presents a disk 33″
in diameter. By the 16th, however,
Jupiter is unobservable to the naked
eye and a poor telescopic target. (The
planet is in conjuction with the Sun on
January 28th.)
Any telescope shows the four big
Galilean moons, and binoculars usually
show at least two or three. The moons
orbit Jupiter at different rates, changing
positions along an almost straight line
from our point of view on Earth. Use
the diagram at right to identify them
by their relative positions on any given
date and time.
All the observable January interactions between Jupiter and its satellites
and their shadows are tabulated below.
Find events timed for dusk in your time
zone, when Jupiter is at its highest.
Features on Jupiter appear closer
to the central meridian than to the
limb for 50 minutes before and after
transiting.
Here are the times, in Universal
Time, when the Great Red Spot should
cross Jupiter's central meridian. The
dates, also in UT, are in bold. (Eastern
Standard Time is UT minus 5 hours.)
December 1: 3:55, 13:51, 23:46;
2: 9:42, 19:38; 3: 5:34, 15:30; 4: 1:26,
11:22, 21:17; 5: 7:13, 17:09; 6: 3:05,
13:01, 22:56; 7: 8:53, 18:48; 8: 4:44,
14:40; 9: 0:36, 10:32, 20:27; 10: 6:23,
16:19; 11: 2:15, 12:11, 22:07; 12: 8:03,
17:58; 13: 3:54, 13:50, 23:46; 14: 9:42,
19:38; 15: 5:34, 15:29; 16: 1:25, 11:21,
21:17; 17: 7:13, 17:09; 18: 3:05, 13:00,
22:56; 19: 8:52, 18:48; 20: 4:44, 14:40;
21: 0:36, 10:31, 20:27; 22: 6:23, 16:19;
23: 2:15, 12:11, 22:06; 24: 8:02, 17:58;
25: 3:54, 13:50, 23:45; 26: 9:42, 19:37;
27: 5:33, 15:29; 28: 1:25, 11:21, 21:16;
29: 7:13, 17:08; 30: 3:04, 13:00, 22:56;
31: 8:52, 18:47
January 1: 4:47, 14:43; 2: 0:39,
10:34, 20:30; 3: 6:26, 16:22; 4: 2:18,
12:14, 22:09; 5: 8:05, 18:01; 6: 3:57,
13:53, 23:48; 7: 9:44, 19:40; 8: 5:36,
15:32; 9: 1:28, 11:24, 21:19; 10: 7:15,
17:11; 11: 3:07, 13:03, 22:59; 12: 8:55,
18:50; 13: 4:46, 14:42; 14: 0:38, 10:34,
20:30; 15: 6:26, 16:21; 16: 2:17, 12:13,
22:09
These times assume that the spot
will be centered at System II longitude
349° on January 1st. If the Red Spot
has moved elsewhere, it will transit 12/3
minutes earlier for each degree less than
349° and 12/3 minutes later for each
degree more than 349°.
Jupiter's Moons
Jan 1
2
Phenomena of Jupiter's Moons, January 2021
Jan. 1
1:58
2:17
5:05
11:15
18:52
21:59
23:34
IV.Oc.D
I.Oc.D
I.Ec.R
IV.Ec.R
III.Oc.D
II.Oc.D
I.Tr.I
0:02
0:21
1:46
1:51
2:19
20:47
23:33
I.Sh.I
III.Ec.R
II.Ec.R
I.Tr.E
I.Sh.E
I.Oc.D
I.Ec.R
16:34
17:28
18:05
18:31
19:28
20:22
20:22
20:48
II.Tr.I
II.Sh.I
I.Tr.I
I.Sh.I
II.Tr.E
I.Tr.E
II.Sh.E
I.Sh.E
Jan. 4
15:18
18:02
I.Oc.D
I.Ec.R
Jan. 5
9:02
III.Tr.I
Jan. 2
Jan. 3
10:41
11:23
12:35
12:35
12:59
14:17
14:52
15:03
15:16
III.Sh.I
II.Oc.D
III.Tr.E
I.Tr.I
I.Sh.I
III.Sh.E
I.Tr.E
II.Ec.R
I.Sh.E
Jan. 6
9:49
12:31
I.Oc.D
I.Ec.R
Jan. 7
6:00
6:46
7:05
7:28
8:54
9:22
9:41
9:45
II.Tr.I
II.Sh.I
I.Tr.I
I.Sh.I
II.Tr.E
I.Tr.E
II.Sh.E
I.Sh.E
4:19
7:00
23:21
I.Oc.D
I.Ec.R
III.Oc.D
0:48
1:36
1:57
II.Oc.D
I.Tr.I
I.Sh.I
Jan. 8
Jan. 9
3:53
4:14
4:21
4:21
10:43
13:58
15:26
18:45
22:50
I.Tr.E
I.Sh.E
II.Ec.R
III.Ec.R
IV.Tr.I
IV.Sh.I
IV.Tr.E
IV.Sh.E
I.Oc.D
1:29
19:27
20:06
20:06
20:25
22:21
22:23
22:42
23:00
I.Ec.R
II.Tr.I
II.Sh.I
I.Tr.I
I.Sh.I
II.Tr.E
I.Tr.E
I.Sh.E
II.Sh.E
Jan. 11
17:21
19:57
I.Oc.D
I.Ec.R
Jan. 12
13:32
14:12
14:37
14:41
14:54
III.Tr.I
II.Oc.D
I.Tr.I
III.Sh.I
I.Sh.I
Jan. 10
3
4
16:54
17:06
17:11
17:38
18:17
I.Tr.E
III.Tr.E
I.Sh.E
II.Ec.R
III.Sh.E
Jan. 13
11:51
14:26
I.Oc.D
I.Ec.R
7
Jan. 14
8:53
9:07
9:22
9:24
11:24
11:40
11:47
12:19
II.Tr.I
I.Tr.I
I.Sh.I
II.Sh.I
I.Tr.E
I.Sh.E
II.Tr.E
II.Sh.E
8
Jan. 15
6:22
8:55
I.Oc.D
I.Ec.R
12
Jan. 16
3:37
3:37
3:51
3:51
5:55
6:08
6:56
8:22
II.Oc.D
I.Tr.I
I.Sh.I
III.Oc.D
I.Tr.E
I.Sh.E
II.Ec.R
III.Ec.R
Every day, interesting events happen between Jupiter's satellites and the planet's disk or shadow. The first columns give
the date and mid-time of the event, in Universal Time (which is 4 hours ahead of Eastern Daylight Time). Next is the satellite
involved: I for Io, II Europa, III Ganymede, or IV Callisto. Next is the type of event: Oc for an occultation of the satellite behind
Jupiter's limb, Ec for an eclipse by Jupiter's shadow, Tr for a transit across the planet's face, or Sh for the satellite casting its
own shadow onto Jupiter. An occultation or eclipse begins when the satellite disappears (D) and ends when it reappears (R ).
A transit or shadow passage begins at ingress (I) and ends at egress (E ). Each event is gradual, taking up to several minutes.
Predictions courtesy IMCCE / Paris Observatory.
WEST
EAST
Europa
5
Ganymede
6
9
Callisto
10
11
13
14
15
Io
16
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 0 h (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.
sk yandtelescope.org * JANUARY 2 021
51
http://www.skyandtelescope.org
Sky & Telescope - January 2021
Table of Contents for the Digital Edition of Sky & Telescope - January 2021
Contents
Sky & Telescope - January 2021 - Cover1
Sky & Telescope - January 2021 - Cover2
Sky & Telescope - January 2021 - 1
Sky & Telescope - January 2021 - Contents
Sky & Telescope - January 2021 - 3
Sky & Telescope - January 2021 - 4
Sky & Telescope - January 2021 - 5
Sky & Telescope - January 2021 - 6
Sky & Telescope - January 2021 - 7
Sky & Telescope - January 2021 - 8
Sky & Telescope - January 2021 - 9
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Sky & Telescope - January 2021 - 11
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Sky & Telescope - January 2021 - Cover3
Sky & Telescope - January 2021 - Cover4
Sky & Telescope - January 2021 - SA1
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Sky & Telescope - January 2021 - SA3
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Sky & Telescope - January 2021 - SA9
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