Sky & Telescope - April 2021 - 50
APRIL 2021 OBSERVING
Celestial Calendar
Action at Jupiter
+5°
δ
26
Mar 20 23
17
0°
Apr
1 4
29
7
10
22
16
Meti
f 9
o
h
Pat
28
BY MID-APRIL Jupiter rises around 5
May 10
4
s
3
γ
VIRGO
-5°
13h 20m
θ
Star magnitudes
ζ
13h 00m
4
5
6
7
8
9
12h 40m
Metis: A Minor Planet for
Small Telescopes
REACHING OPPOSITION ON April 4th, asteroid 9 Metis provides an opportunity
for amateurs to explore beyond the " big four " (Ceres, Pallas, Juno, and Vesta) and
observe a lesser-known but still bright asteroid. Metis reaches magnitude 9.5 in
Virgo and sits about 6° northwest of the tight double star Gamma (Ȗ) Virginis (Porrima). The asteroid travels westward in retrograde motion this month and is well
placed for observing as soon as the sky gets dark. Meanwhile, 6.5-magnitude Vesta is
next door in Leo. (Turn to page 48 of the March issue for a Vesta finder chart.)
Metis is a moderately large object about 235 kilometers (146 miles) across with
an irregular, elongated shape. It's related compositionally to 113 Amalthea, and
both are believed to be the surviving fragments of a much larger Vesta-sized asteroid that broke up about a billion years ago.
Irish astronomer Andrew Graham discovered Metis in April 1848, and for 160
years it remained the only minor planet discovered from Irish soil. The drought
ended in October 2008, when amateur astronomer Dave McDonald found 19thmagnitude 2008 TM9 from his home in County Kildare, west of Dublin.
Selected Jupiter Mutual Satellite Events
Date
50
Time (UT)
Event
Mag change
April 1
13:17 - 13:23
Ganymede occults Io
0.6
April 6
11:46 - 11:51
Europa eclipses Io
0.3
April 11
10:01 - 10:11
Io eclipses Callisto
0.4
April 12
11:51 - 12:13
Io eclipses Callisto
0.5
April 15
10:08 - 10:16
Ganymede eclipses Europa
0.5
April 18
9:52 - 9:58
Io eclipses Europa
0.6
April 25
12:06 - 12:11
Io eclipses Europa
0.6
April 29
12:13 - 12:27
Ganymede eclipses Callisto
0.4
APRIL 2 021 * SK Y & TELESCOPE
a.m. local daylight-saving time and has
an altitude of nearly 20° by the time
morning twilight extinguishes all but
the very brightest stars. On the 15th,
the planet displays a disk 36″ across and
beams at magnitude -2.1 from easternmost Capricornus.
Any telescope will reveal the four
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 April 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.)
March 1: 9:01, 18:57; 2: 4:53, 14:48;
3: 0:44, 10:40, 20:36; 4: 6:32, 16:27;
5: 2:23, 12:19, 22:15; 6: 8:11, 18:06; 7:
4:02, 13:58, 23:54; 8: 9:50, 19:45; 9:
5:41, 15:37; 10: 1:33, 11:29, 21:24; 11:
7:20, 17:16; 12: 3:12, 13:07, 23:03; 13:
8:59, 18:55; 14: 4:51, 14:46; 15: 0:42,
10:38, 20:34; 16: 6:03, 16:25; 17: 2:21,
12:17, 22:13; 18: 8:09, 18:04; 19: 4:00,
13:56, 23:52; 20: 9:47, 19:43; 21: 5:39,
15:35; 22: 1:31, 11:26, 21:22; 23: 7:18,
17:14; 24: 3:10, 13:05, 23:01; 25: 8:57,
18:53; 26: 4:48, 14:44; 27: 0:40, 10:36,
20:31; 28: 6:27, 16:23; 29: 2:19, 12:15,
22:10; 30: 8:06, 18:02; 31: 3:58, 13:53,
23:49
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,
Sky & Telescope - April 2021
Table of Contents for the Digital Edition of Sky & Telescope - April 2021
Contents
Sky & Telescope - April 2021 - Cover1
Sky & Telescope - April 2021 - Cover2
Sky & Telescope - April 2021 - 1
Sky & Telescope - April 2021 - Contents
Sky & Telescope - April 2021 - 3
Sky & Telescope - April 2021 - 4
Sky & Telescope - April 2021 - 5
Sky & Telescope - April 2021 - 6
Sky & Telescope - April 2021 - 7
Sky & Telescope - April 2021 - 8
Sky & Telescope - April 2021 - 9
Sky & Telescope - April 2021 - 10
Sky & Telescope - April 2021 - 11
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Sky & Telescope - April 2021 - Cover3
Sky & Telescope - April 2021 - Cover4
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