My first Magazine Sky & Telescope - 04.2019 | Page 52

APRIL 2019 OBSERVING
Celestial Calendar
Action at Jupiter
JUPITER RISES about 1 a.m. local
Another Asteroid
–10°
4
May 2
VIRGO
28
30
26
24
M104
20
22
18
–12°
P
6
4
of
16
12
14
10
8
Y 1669
Apr
2
d
–16°
b
magnitudes
–14° 29
27
31
ath
Iris
3
4
5
6
7
8
9
CORVUS
–18°
12 h 50 m
12 h 40 m
ONCE YOU’VE WARMED UP with Pal-
las, turn your scope to the southwest
to fi nd asteroid 7 Iris. This small object
— it sports a diameter of about 200 km,
less than half that of Pallas — reaches
opposition on April 5th. On that date,
Iris is curling through northeastern
Corvus, headed toward Virgo. Serendipi-
tously, several stars lie on or near the
asteroid’s path. Use Spica or Delta (δ)
Corvi to fi nd Iris’s general location; the
multiple star Struve 1669 (Σ1669) is a
good place to start your fi nal star-hop.
Iris is the fourth-brightest asteroid,
but intrinsic brightness doesn’t always
translate to easy visibility. At opposi-
50
A PR I L 2 019 • SK Y & TELESCOPE
12 h 30 m
12 h 20 m
p Asteroid 7 Iris heads into Virgo in the last half
of April. Star-hop from Spica or Delta (δ) Corvi
to the multiple-star system Σ1669; from there,
start your hunt for the 9th-magnitude asteroid.
tion, Iris shines only at magnitude 9.4,
still within range of small scopes but far
dimmer than the 6.9-magnitude light
we saw in 2017. Mark your calendars for
October 2028, when Iris is predicted to
shine at magnitude 7.0.
Iris becomes visible for observers at
mid-northern latitudes in mid-evening
and reaches an altitude of some 20°
in the southeast before 10 p.m. local
daylight-saving time. Iris is highest,
around 35°, in the hour after midnight.
daylight-saving time at the beginning
of April. The giant planet, beaming at
magnitude –2.3, is diffi cult to miss as
it rises in the southeast with Ophiu-
chus. Jupiter grows even brighter over
the course of the month, reaching
magnitude –2.5 by April 30th. Jupiter’s
equatorial diameter also expands from
40″ to 43″ in April.
Any telescope shows the four big
Galilean moons, and binoculars usu-
ally show at least two or three. Use the
diagram on the facing page to identify
them at any date and time.
All of the April interactions between
Jupiter and its satellites and their shad-
ows are tabulated on the facing page.
Find events timed for when Jupiter is at
its highest in the early morning hours.
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: 7:14, 17:10; 2: 3:05, 13:01,
22:57; 3: 8:52, 18:48; 4: 4:44, 14:40;
5: 0:35, 10:31, 20:27; 6: 6:22, 16:18;
7: 2:14, 12:09, 22:05; 8: 8:01, 17:56; 9:
3:52, 13:48, 23:43; 10: 9:39, 19:35; 11:
5:31, 15:26; 12: 1:22, 11:18, 21:13; 13:
7:09, 17:05; 14: 3:00, 12:56, 22:52; 15:
8:47, 18:43; 16: 4:39, 14:34; 17: 0:30,
10:26, 20:21; 18: 6:17, 16:13; 19: 2:08,
12:04, 22:00; 20: 7:55, 17:51; 21: 3:47,
13:42, 23:38; 22: 9:34, 19:29; 23: 5:25,
15:21; 24: 1:16, 11:12, 21:08; 25: 7:03,
16:59; 26: 2:55, 12:50, 22:46; 27: 8:42,
18:37; 28: 4:33, 14:29; 29: 0:24, 10:20,
20:15; 30: 6:11, 16:07; 31: 2:02, 11:58,
21:54.
April 1: 7:49, 17:45; 2: 3:41, 13:36,
23:32; 3: 9:28, 19:23; 4: 5:19, 15:14;
5: 1:10, 11:06, 21:01; 6: 6:57, 16:53; 7:
2:48, 12:44, 22:40; 8: 8:35, 18:31; 9:
4:26, 14:22; 10: 0:18, 10:13, 20:09; 11:
6:05, 16:00; 12: 1:56, 11:51, 21:47; 13:
7:43, 17:38; 14: 3:34, 13:30, 23:25; 15:
9:21, 19:16; 16: 5:12, 15:08; 17: 1:03,
10:59, 20:55; 18: 6:50, 16:46; 19: 2:41,
12:37, 22:33; 20: 8:28, 18:24; 21: 4:19,
14:15; 22: 0:11, 10:06, 20:02; 23: 5:57,
15:53; 24: 1:49, 11:44, 21:40; 25: 7:35,