Sky & Telescope - December 2020 - 50

DECEMBER 2020 OBSERVING
Celestial Calendar

Action at Jupiter

The Moon Eclipses Venus
ON DECEMBER 12TH, two days before

the solar eclipse, skywatchers in western North America, Alaska, Hawai'i,
and eastern Russia will see a sliver
crescent Moon occult the planet Venus.
The event takes place during daylight
hours, except in Russia where it occurs
before sunrise.
Because the Moon will be just 5%
illuminated and 25° west of the Sun,
you'll likely need binoculars to ﬁnd
the pale lunar crescent. Telescopes will
show a tiny, but brilliant, gibbous Venus
near the Moon before and after the
occultation.
If you live in the Paciﬁc time zone or
points west, Venus and the Moon make
a beautiful sight at dawn, separated by
only 2½°. Observers on the East Coast
will see the pair 4° apart. Unfortunately, in the eastern half of North

Lunar Occultation of Venus
City

Disappearance /
Reappearance

Altitude*

Denver, CO

2:29 p.m. /
-

7°

Mazatlán
(Mexico)

2:48 p.m. /
-

12°

San Francisco,
CA

1:11 p.m. /
2:18 p.m.

21°

Vancouver, BC
(Canada)

1:02 p.m. /
1:48 p.m.

14°

Anchorage, AK

11:14 a.m. /
12:04 p.m.

11°

Honolulu, HI

10:13 a.m. /
11:36 a.m.

50°

*Altitude of Venus at disappearance. All times local.

50

DECEMBER 2 02 0 * SK Y & TELESCOPE

America the pair set before the occultation begins.
We've included occultation times for
several cities in the table below. You can
determine the details for other locations
with most planetarium software packages, including the excellent freeware
program Stellarium (stellarium.org).
Simply dial up the correct date, use the
search function for "Venus," and then
advance the time until the illuminated
lunar limb touches the planet. (It's
important to remember to uncheck the
"Scale Moon" box in the Sky and viewing options menu so the Moon appears
the correct size.) Venus will reappear at
the lunar dark limb about an hour after
it disappears.

Minima of Algol
Nov.
1
4
7
10
13
16
18
21
24
27
30

UT
17:56
14:44
11:33
8:22
5:11
2:00
22:49
19:38
16:27
13:16
10:05

Dec.
3
6
9
11
14
17
20
23
26
29
31

UT
6:54
3:43
0:32
21:21
18:10
14:59
11:49
8:38
5:27
2:16
23:05

These geocentric predictions are from the
recent heliocentric elements Min. = JD
2445641.554 + 2.867324E, where E is any
integer. For a comparison-star chart and
more info, see skyandtelescope.org/algol.

is reasonably high in the southwest
at dusk and sets around 8:00 p.m.
local time. The best time to observe
the planet is early in twilight, when
it's highest. On December 1st, Jupiter
shines brightly at magnitude -2.0 and
presents a disk 34″ in diameter.
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 on the facing page to
identify them by their relative positions
on any given date and time.
All the December interactions
between Jupiter and its satellites and
their shadows are tabulated on the facing page.
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.)
November 1: 8:05, 18:45; 2: 4:42,
14:37; 3: 0:33, 10:29, 20:25; 4: 6:21,
16:16; 5: 2:12, 12:08, 22:04; 6: 7:59,
17:55; 7: 3:51, 13:47, 23:43; 8: 9:39,
19:34; 9: 5:31, 15:26; 10: 1:22, 11:18,
21:14; 11: 7:10, 17:05; 12: 3:01, 12:57,
22:53; 13: 8:49, 18:44; 14: 4:41, 14:36;
15: 0:32, 10:28, 20:24; 16: 6:02, 16:15;
17: 2:11, 12:07, 22:03; 18: 7:59, 17:55;
19: 3:51, 13:46, 23:42; 20: 9:38, 19:34;
21: 5:30, 15:25; 22: 1:21, 11:17, 21:13;
23: 7:09, 17:05; 24: 3:01, 12:56, 22:52;
25: 8:48, 18:44; 26: 4:40, 14:36; 27:
0:32, 10:27, 20:23; 28: 6:19, 16:15; 29:
2:11, 12:06, 22:02; 30: 7:58, 17:54
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,

STELL A RIU M

AT THE START OF DECEMBER, Jupiter
http://www.stellarium.org http://www.skyandtelescope.org/algol
Sky & Telescope - December 2020

Table of Contents for the Digital Edition of Sky & Telescope - December 2020
