Sky & Telescope - August 2024 - 50

AUGUST 2024 OBSERVING
Celestial Calendar
Action at Jupiter
21h 10m
-6°
AQUARIUS
-8°
July
23
25 27 29 31
Aug
2
21h 00m
20h 50m
4
3
20h 40m
3
4
5
6
7
8
9
4 6 8 10 12 14 16 18 20 22 24 26 28 30 Sept
µ
ε
Albali
-10°
5
ν
7009
-12°
M73
M72
Saturn Nebula
1
3
JUPITER IS NOW a prominent sight in
the morning sky. During mid-August
it rises at around 1 a.m. local daylight
time and climbs to an altitude of 56° by
sunrise. On the 15th, the planet shines
at magnitude -2.2 and presents a disk
36.8″ across. For the sake of comparison,
when it reaches opposition on
December 7th, it will have brightened
to -2.8 and grown to 48.2″ diameter.
Between then and now, the big planet
shifts just a bit more than ½° eastward
against the background stars in Taurus.
In that same span of time, Mars - Jupiter's
close August companion - motors
an impressive 50° eastward!
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
interactions between Jupiter and its
satellites and their shadows are tabulated
on the facing page.
Features on Jupiter appear closer to
Rainbow Goddess Asteroid
in Aquarius
IN GREEK MYTHOLOGY, Iris is the
goddess of the rainbow. It's also the
name of a lovely flower, and the
seventh asteroid discovered. Iris (the
asteroid, that is) comes to opposition
on August 6th, when it shines at
magnitude 8.3 - placing it within easy
reach of a small telescope and even
binoculars from dark locations.
As the chart above shows, during
August the stony asteroid ambles
westward across western Aquarius.
(The asteroid's position is plotted for
0h UT on the dates indicated.) On the
2nd Iris passes less than 3° north of
the Saturn Nebula (NGC 7009) before
slipping just 6′ north of 4.7-magnitude
Mu (μ) Aquarii on the night of the
11th. From that date through to the
18th, the asteroid traverses the 1.3°
distance between Mu and 3.8-magnitude
Epsilon (ε) Aquarii, giving us an
50 AUGUST 2024 * SKY & TELESCOPE
entire week during which we can easily
gauge the object's nightly motion.
Discovered by English astronomer
John R. Hind on August 13, 1847, Iris is
a 200-km-wide, main-belt stony asteroid
rich in silicates. In the February
2024 article published in The Planetary
Science Journal, " Detection of Molecular
H2O on Nominally Anhydrous Asteroids, "
a team of scientists described
how they obtained infrared spectra of
several asteroids from aboard the nowretired
Stratospheric Observatory for
Infrared Astronomy (SOFIA) aircraft.
Both Iris and 20 Massalia unequivocally
revealed the signature of water - the
first such detection on otherwise " dry "
main-belt asteroids. Just knowing water
is present in some form on Iris makes
watching it drift through Aquarius, the
Water Bearer appropriately enough,
even more compelling.
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.)
July 1: 9:46, 19:42; 2: 5:38, 15:34;
3: 1:30, 11:25, 21:21; 4: 7:17, 17:13; 5:
3:09, 13:04, 23:00; 6: 8:56, 18:52; 7:
4:48, 14:43; 8: 0:39, 10:35, 20:31; 9:
6:26, 16:22; 10: 2:18, 12:14, 22:10; 11:
8:05, 18:01; 12: 3:57, 13:53, 23:49; 13:
9:44, 19:40; 14: 5:36, 15:32; 15: 1:27,
11:23, 21:19; 16: 7:15, 17:11; 17: 3:06,
13:02, 22:58; 18: 8:54, 18:50; 19: 4:45,
14:41; 20: 0:37, 10:33, 20:28; 21: 6:24,
16:20; 22: 2:16, 12:11, 22:07; 23: 8:03,
17:59; 24: 3:55, 13:50, 23:46; 25: 9:42,
19:38; 26: 5:33, 15:29; 27: 1:25, 11:21,
21:16; 28: 7:12, 17:08; 29: 3:04, 12:59,
22:55; 30: 8:51, 18:47; 31: 4:43, 14:38
August 1: 0:38, 10:33, 20:29; 2:
6:25, 16:21; 3: 2:16, 12:12, 22:08; 4:
8:04, 17:59; 5: 3:55, 13:51, 23:47; 6:
9:42, 19:38; 7: 5:34, 15:30; 8: 1:25,
11:21, 21:17; 9: 7:13, 17:08; 10: 3:04,
Path o
7f Iris
Star magnitudes
Sky & Telescope - August 2024

Table of Contents for the Digital Edition of Sky & Telescope - August 2024
