Sky & Telescope - October 2021 - 50

OCTOBER 2021 OBSERVING
Celestial Calendar
Action at Jupiter
The aurora is fickle. Sometimes the
lights arrive early, sometimes late, or
sometimes not at all. We can't always
be certain which way the magnetic field
of the plasma blast will be oriented at
arrival time. But don't be discouraged -
our understanding of this spellbinding
and complex phenomenon is imperfect.
" The hardest part of forecasting is
predicting the Bz, " says Onsager. " We
only get 45 minutes lead time from
DSCOVR. It's very complicated and
difficult to determine the Bz en route
from the Sun. "
The best time to watch for the
pSolar flares are one key source of the Sun's
plasma reaching Earth. These are explosive
events that propel material into space at extreme
speeds. Only those that direct particles
at our planet possess the potential to produce
an auroral display.
is NOAA's Real Time Solar Wind live
feed at https://is.gd/noaa_solarwind.
Bz is the topmost graph on the page.
When the Bz dips below the centerline
to −5° or more, a bundle of southdirected
plasma is approximately 45 to
60 minutes from banging into Earth's
magnetosphere. Add in another 15 to
30 minutes for reconnection on the
nightside . . . and Pants On!
Minima of Algol
Sept.
UT
1
4
7
10
13
16
18
21
24
27
30
16:29
13:18
10:07
6:55
3:44
0:32
21:21
18:10
14:58
11:47
8:36
Oct.
3
6
8
11
14
17
20
23
26
29
31
northern lights is from about 10 p.m.
to 2 a.m. local standard time (11 p.m.
to 3 a.m. local daylight-saving time),
with the sweet spot lasting from about
11 p.m. to 1 a.m. A display often
begins with little fanfare as a low, pale
green arc 5° to 10° above the northern
horizon. If the arc brightens or a
second arc forms, stick around - you
may soon witness a pretty display of
feathery plumes slowly parading across
the bottom third of the northern sky.
If the predicted Kp is high and the sky
explodes with auroral splendor, forget
about going to bed - you may find
yourself in the throes of that hoped for
" one-of-a-kind " experience.
29
UT
5:24
2:13
23:02
19:50
16:39
13:28
10:17
7:05
3:54
0:43
21:32
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.
18
30
PERSEUS
38
Algol
21
AS OCTOBER OPENS, Jupiter rises well
before sunset and reaches the meridian
at about 10 p.m. local daylight-saving
time, when it's well placed for telescopic
viewing. The giant planet shines at
magnitude -2.7 from eastern Capricornus
and presents a disk 46″ across.
Any telescope reveals 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 observable
interactions between Jupiter and its
satellites and their shadows are listed
on the facing page. Find events timed
for when Jupiter is at its highest.
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
Daylight Time is UT minus 4 hours.)
September 1: 1:17, 11:13, 21:09;
2: 7:04, 16:59; 3: 2:55, 12:51, 22:47;
4: 8:42, 18:38; 5: 4:33, 14:29; 6: 0:25,
10:20, 20:16; 7: 6:11, 16:07; 8: 2:03,
11:58, 21:54; 9: 7:50, 17:45; 10: 3:41,
13:37, 23:32; 11: 9:28, 19:23; 12: 5:19,
15:15; 13: 1:10, 11:06, 21:02; 14: 6:57,
16:53; 15: 2:48, 12:44, 22:40; 16: 8:35,
18:31; 17: 4:27, 14:22; 18: 0:18, 10:14,
20:09; 19: 6:05, 16:01; 20: 1:56, 11:52,
21:48; 21: 7:43, 17:39; 22: 3:34, 13:30,
23:26; 23: 9:21, 19:17; 24: 5:13, 15:08;
25: 1:04, 10:59, 20:55; 26: 6:51, 16:47;
27: 2:42, 12:38, 22:34; 28: 8:29, 18:25;
29: 4:21, 14:17; 30: 0:12, 10:08, 20:04
October 1: 6:03, 15:58; 2: 1:54,
TRIANGULUM
34
pWith the end of summer in the Northern
Hemisphere, Perseus climbs in the northeastern
sky in the evening. Every 2.7 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).
50 OCTOBER 2021 * SKY & TELESCOPE
11:50, 21:45; 3: 7:41, 17:37; 4: 3:32,
13:28, 23:24; 5: 9:19, 19:15; 6: 5:11,
15:07; 7: 1:02, 10:58, 20:54; 8: 6:49,
16:45; 9: 2:41, 12:36, 22:32; 10: 8:28,
18:24; 11: 4:19, 14:15; 12: 0:11, 10:06,
20:02; 13: 5:58, 15:54; 14: 1:49, 11:45,
21:41; 15: 7:36, 17:32; 16: 3:28, 13:24,
23:19; 17: 9:15, 19:11; 18: 5:07, 15:02;
19: 0:58, 10:54, 20:49; 20: 6:45,
16:41; 21: 2:37, 12:32, 22:28; 22: 8:24,
18:20; 23: 4:15, 14:11; 24: 0:07, 10:03,
19:58; 25: 5:54, 15:50; 26: 1:46, 11:41,
NASA / GODDARD / SDO
https://www.is.gd/noaa_solarwind http://www.skyandtelescope.org/algol
Sky & Telescope - October 2021

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