Sky & Telescope - May 2021 - 50

MAY 2021 OBSERVING
Celestial Calendar

Action at Jupiter
BY MID-MAY JUPITER rises around

Simon Kidd

WinJUPOS simulation

S MERCURY PAIR Simon Kidd made this remarkable photo of Mercury (left) with a C14 telescope
equipped with a ZWO ASI224MC camera and 742-nm infrared (IR) filter on June 25, 2018. Compare it to the WinJUPOS simulation based on MESSENGER imagery. Kidd captured at least a half
dozen rayed craters and several intercrater plains in his image.

your setting circles to agree with the
R.A. and Dec. of the Sun's position,
then shift your mount so that Mercury's coordinates are displayed. Even
if you're not precisely polar aligned, the
offset between Mercury and the Sun is
small enough that the planet should lie
within the ﬁeld of view of a low-power
eyepiece. Remove the solar ﬁlter and
examine the planet at the highest magniﬁcation conditions will allow.
French amateur Michel Legrande
calls Mercury " a difﬁcult planet. " He
goes on to add, " experience has taught
me to observe as often as possible . . .
the eye, like a muscle, must be trained. "
He uses an 8.26-inch (210-mm) f/6
homebuilt Newtonian reﬂector and
magniﬁcations between 140× and 200×
for his Mercury observing.
Amateur and professional astronomers have recorded vague streaks and
spots for decades. Now, thanks to
detailed images from NASA's MESSENGER mission, we can correlate what

we see in our telescopes with features
depicted in the photos. Amateurs have
had even better success capturing Mercurian detail in daylight with digital
cameras equipped with red or infrared ﬁlters. Using the free WinJUPOS
program (downloadable at jupos.org),
images or sketches can be compared to
the planet's appearance to conﬁrm and
identify speciﬁc features such as bright
rayed craters and dark, volcanic plains.
Simon Kidd of Cottered, England,
who uses a C14 Schmidt-Cassegrain
telescope and a 742-nm infrared ﬁlter
to image the planet, offers this advice:
" Don't give up, even if the conditions
are only average. There are bound to
be a few good frames if you capture
100,000 or so in one run. Keep the
exposure really short - a few milliseconds maximum. "
For additional information about
observing and photographing Mercury,
visit the ALPO Mercury Section website
at https://is.gd/ALPOMercury.

Selected Jupiter Mutual Satellite Events

50

Date

Time (UT)

Event

Mag change

May 1

7:39 - 7:41

Europa eclipses Io

0.9

May 11

9:06 - 9:15

Europa eclipses Ganymede

0.3

May 20

7:56 - 8:01

Io eclipses Europa

0.4

May 27

10:12 - 10:17

Io eclipses Europa

0.5

M AY 2 0 2 1 * S K Y & T E L E S C O P E

2 a.m. local daylight-saving time and
ascends to an altitude of nearly 30°
in the south-southeast by the time
morning twilight brightens the sky. On
the 15th, the planet displays a disk 39″
across and beams at magnitude -2.3.
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 tabulated on the facing page. Find events timed for dawn in
your time zone, when Jupiter is 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.)
April 1: 9:47, 19:42; 2: 5:38, 15:34;
3: 1:30, 11:25, 21:21; 4: 7:17, 17:13; 5:
3:08, 13:04, 22:59; 6: 8:56, 18:51; 7:
4:47, 14:43; 8: 0:39, 10:34, 20:30; 9:
6:26, 16:22; 10: 2:18, 12:13, 22:09; 11:
8:05, 18:00; 12: 3:56, 13:52, 23:48; 13:
9:43, 19:39; 14: 5:35, 15:31; 15: 1:27,
11:22, 21:18; 16: 7:14, 17:09; 17: 3:05,
13:01, 22:57; 18: 8:52, 18:48; 19: 4:44,
14:40; 20: 0:35, 10:31, 20:27; 21: 6:23,
16:18; 22: 2:14, 12:10, 22:05; 23: 8:01,
17:57; 24: 3:53, 13:48, 23:44; 25: 9:40,
19:36; 26: 5:31, 15:27; 27: 1:23, 11:19,
21:14; 28: 7:10, 17:06; 29: 3:01, 12:57,
22:53; 30: 8:49, 18:44
May 1: 4:43, 14:39; 2: 0:35, 10:30,
20:26 3: 6:22, 16:18; 4: 2:13, 12:09,
22:05 5: 8:01, 17:56; 6: 3:52, 13:48, 23:43
7: 9:39, 19:35; 8: 5:30, 15:26; 9: 1:22,
11:18, 21:13 10: 7:09, 17:05; 11: 3:00,
12:56, 22:52 12: 8:48, 18:43; 13: 4:39,
14:35; 14: 0:30, 10:26, 20:22 15: 6:17,
16:13; 16: 2:09, 12:04, 22:00 17: 7:56,
17:52; 18: 3:47, 13:43, 23:39 19: 9:34,
http://www.jupos.org https://www.is.gd/ALPOMercury
Sky & Telescope - May 2021

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