Sky & Telescope - February 2021 - 51

Action at Jupiter
JUPITER WAS IN CONJUNCTION with

the Sun on January 29th, rendering it
unobservable for the latter part of January and for much of February. (Both
Jupiter tables and the Jupiter's Moons
diagram presented here omit dates
when the planet is out of view.) Jupiter
returns to the dawn sky as a naked-eye
object around February 19th, when it
will shine at magnitude -1.9 and present a disk 33″ in diameter. Binocular
users will likely be able to spot the
planet earlier.
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 February interactions between Jupiter and its satellites
and their shadows are tabulated in the
table below right. Find events timed for
dawn in your time zone when Jupiter
is at its highest. For much of February,
the events listed here will be difﬁcult to
view, owing to the planet's low altitude.

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.)
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
February 19: 0:42, 10:38, 20:34;
20: 6:30, 16:26; 21: 2:22, 12:17,
22:13; 22: 8:09, 18:05; 23: 4:01,
13:56, 23:52; 24: 9:48, 19:44; 25:
5:40, 15:35; 26: 1:31, 11:27, 21:23;
27: 7:19, 17:14; 28: 3:10, 13:06, 23:02
These times assume that the spot
will be centered at System II longitude 353° on February 1st. If the
Red Spot has moved elsewhere, it
will transit 12/3 minutes earlier for
each degree less than 353° and 12/3
minutes later for each degree more
than 353°.

Jupiter's Moons
Feb 19
20

WEST

EAST

21
22

Europa

23
24

Ganymede

25
26

Io

27
28
Mar 1

Callisto

2
3

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.

Phenomena of Jupiter's Moons, February 2021
Feb. 19

29
30

18

PERSEUS

Feb. 20

38

Algol

21

TRIANGULUM

Feb. 21

34

S Perseus approaches the zenith during evening hours in February. Every 2.87 days, Algol
(Beta Persei) dips from its usual magnitude 2.1
to 3.4 and back. Use this chart to estimate its
brightness in respect to comparison stars of
magnitude 2.1 (Gamma Andromedae) and 3.4
(Alpha Trianguli).

1:28
2:13
16:11
18:52

II.Sh.E
II.Tr.E
I.Ec.D
I.Oc.R

12:53
13:22
13:45
15:39
16:03
16:57
20:37
21:28

IV.Ec.D
I.Sh.I
I.Tr.I
I.Sh.E
I.Tr.E
II.Ec.D
II.Oc.R
IV.Oc.R

0:47
6:04
10:39

III.Ec.D
III.Oc.R
I.Ec.D

13:23

I.Oc.R

7:50
8:16
10:08
10:33
11:52
12:44
14:47
15:39

I.Sh.I
I.Tr.I
I.Sh.E
I.Tr.E
II.Sh.I
II.Tr.I
II.Sh.E
II.Tr.E

Feb. 23

5:08
7:53

I.Ec.D
I.Oc.R

Feb. 24

2:19
2:46
4:36
5:03

I.Sh.I
I.Tr.I
I.Sh.E
I.Tr.E

Feb. 22

Feb. 25

Feb. 26

6:14
10:02
14:41
16:34
18:19
20:13
23:36

II.Ec.D
II.Oc.R
III.Sh.I
III.Tr.I
III.Sh.E
III.Tr.E
I.Ec.D

2:24
20:47
21:16
23:05
23:34

I.Oc.R
I.Sh.I
I.Tr.I
I.Sh.E
I.Tr.E

1:10
2:10
4:05

II.Sh.I
II.Tr.I
II.Sh.E

5:05
18:05
20:54

II.Tr.E
I.Ec.D
I.Oc.R

Feb. 27

15:16
15:46
17:33
18:04
19:32
23:26

I.Sh.I
I.Tr.I
I.Sh.E
I.Tr.E
II.Ec.D
II.Oc.R

Feb. 28

4:47
10:33
12:34
15:25
20:26

III.Ec.D
III.Oc.R
I.Ec.D
I.Oc.R
IV.Sh.I

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.

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Sky & Telescope - February 2021

Table of Contents for the Digital Edition of Sky & Telescope - February 2021
