Sky & Telescope - September 2021 - 50

SEPTEMBER 2021 OBSERVING
Celestial Calendar
Sept 6, 6:15 am CDT
Latitude = 40° N
Longitude = 90° W
Moon
Altitude = 3.3°
tObserving the very old crescent Moon before
sunrise on September 6th will be challenging.
Use binoculars or a Go To telescope to pinpoint
the thin crescent's location.
For locations farther west the crescent
is unlikely to be seen at all, but
prospects improve slightly in the Eastern
Time Zone. From New York City,
the old lunar crescent stands 3° high at
6:05 a.m., 20 minutes before sunrise.
The Moon will be 14 hours 47 minutes
before new and have an illuminated
extent of 0.5%.
Regardless of location, conditions
Sun altitude = -4.2°
old in his giant 40×150 binoculars on
September 7, 2002. At the time, the
Moon was just 7.5° from the Sun.
On September 6th, meticulous
observers have a chance to spot an
exceedingly old crescent at dawn. From
Des Moines, Iowa (41.6° N, 93.6° W),
the Moon reaches an altitude of 3° at
6:25 a.m. Central Daylight Time, when
it's 13 hours 27 minutes before new.
The crescent will be just 0.5% illuminated
and 7.8° from the Sun, but on the
plus side it will also be 4.7° north of
the ecliptic and five days shy of perigee.
Even so, sighting such a razor-thin lunar
crescent is a challenge requiring tripodmounted
binoculars or a telescope.
Minima of Algol
Sept.
Aug.
1
4
6
9
12
15
18
21
24
26
29
UT
3:35
0:24
21:12
18:01
14:49
11:38
8:27
5:15
2:04
22:52
19:41
1
4
7
10
13
16
18
21
24
27
30
have to be just right with haze-free
skies, an unobstructed view, and, most
importantly, knowing exactly where to
look. Most charting and planetarium
software packages (including the
popular freeware program Stellarium)
will allow you to figure out the circumstances
for your specific location.
Bear in mind that only 75° of the
crescent's 180° arc will be illuminated.
Your best bet is to use a Go To telescope
to lock onto the Moon's position and
then carefully examine the view with
a wide-field eyepiece. Make sure you've
carefully focused the scope on a bright
star beforehand since the smallest
amount of mis-focus will cause the
crescent to completely blend into the
sky. Once you've spotted the Moon in
your scope, try binoculars.
29
UT
16:29
13:18
10:07
6:55
3:44
0:32
21:21
18:10
14:58
11:47
8:36
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
Action at Jupiter
JUPITER REACHED OPPOSITION on
the night of August 19th and as a result
is in prime viewing position from dusk
through the wee hours of the predawn.
You'll have plenty of chances to view
the comings and goings of its four
brightest moons and observe its famous
Great Red Spot. At mid-month Jupiter
gleams at magnitude -2.8 and presents
a disk that spans a generous 48″.
Any telescope reveals the four big
Galilean moons, and binoculars usually
show at least two or three. Use the
diagram on the facing page to identify
them by their relative positions on any
given date and time. All the observable
September interactions between Jupiter
and its satellites and their shadows
are tabulated on the facing page. Find
events timed for dawn 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
Daylight Time is UT minus 4 hours.)
August 1: 0:46, 10:42, 20:38; 2:
TRIANGULUM
34
With 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 SEPTEMBER 2021 * SKY & TELESCOPE
6:33, 16:29; 3: 2:24, 12:20, 22:16; 4:
8:11, 18:07; 5: 4:02, 13:58, 23:54; 6:
9:49, 19:45; 7: 5:40, 15:36; 8: 1:31,
11:27, 21:23; 9: 7:18, 17:14; 10: 3:09,
13:05, 23:01; 11: 8:56, 18:52; 12: 4:47,
14:43; 13: 0:38, 10:34, 20:30; 14: 6:25,
16:21; 15: 2:16, 12:12, 22:08; 16: 8:03,
17:59; 17: 3:54, 13:50, 23:46; 18: 9:41,
19:37; 19: 5:32, 15:28; 20: 1:23, 11:19,
21:15; 21: 7:10, 17:06; 22: 3:01, 12:57,
22:53; 23: 8:48, 18:44; 24: 4:39, 14:35;
25: 0:30, 10:26, 20:22; 26: 6:17, 16:13;
27: 2:08, 12:04, 21:59; 28: 7:55, 17:51;
29: 3:46, 13:42, 23:38; 30: 9:33, 19:29;
31: 5:24, 15:20
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,
GREGG DINDERMAN / S&T
Ecliptic
http://www.skyandtelescope.org/algol
Sky & Telescope - September 2021

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