Sky & Telescope - July 2021 - 50

JULY 2021 OBSERVING
Celestial Calendar
-5°
20h 20m

20h 00m
June 1 17
13
21 25 29
July
3

19h 40m

λ

19h 20m

19h 00m

THE JUPITER OBSERVING SEASON
7

AQUILA

11
15
19

-10°

Star magnitudes

23

CAP

27

α

31
Aug 4
8
12

β

16

-15°

2
3
4
5
6
7
8

20
24

SAGITTARIUS

ρ

1

-20°

28
Sept 1

π

NGC 6716

ο

M75

ξ2

Homing in on Hebe
IN THE MARCH CELESTIAL CALENDAR,

I described how Vesta is the parent body
of a group of meteorites known as the
HED clan. But astronomers may have
uncovered yet another origin story
- this one involving 6 Hebe, which
reaches opposition in southern Aquila
on July 19th.
Hebe is a stony, main-belt asteroid
that measures 205 km across. It's also
the suspected source of two classes of
meteorites: The H-chondrites (the most
common type found on Earth) and
the related, but rarer, IIE irons. Not all
scientists agree that Hebe is the primary source of H-chondrites, arguing

that its craters are too small to have
produced the volume of material found
on Earth. But recent research indicates
some of Hebe's fragmental remains
may have created a small family of
neighboring asteroids that also generate
H-chondrites.
Make your connection with this
fascinating asteroid this summer
when it inches southwest from southern Aquila into northern Sagittarius.
Hebe starts July at magnitude 8.7 and
brightens to 8.3 by the 20th. A pair of
10×50 binoculars should sufﬁce to snag
it under dark skies, otherwise any small
telescope will do the trick.

Selected Jupiter Mutual Satellite Events
Date

Time (UT)

Event

Mag change

11:06 - 11:13

Io eclipses Ganymede

0.3

June 10

7:58 - 8:05

Callisto eclipses Europa

0.9

June 18

5:26 - 5:55

Europa eclipses Callisto

0.6

June 21

6:13 - 6:17

Io eclipses Europa

0.8

8:33 - 8:36

Io eclipses Europa

0.9

10:54 - 10:57

Io eclipses Europa

1.0

June 1

June 28
July 5

50

J U LY 2 0 2 1 * S K Y & T E L E S C O P E

Action at Jupiter
is entering its prime. By mid-July, the
planet rises late in the evening and
reaches the meridian just before the
start of astronomical twilight. On the
15th, the planet displays a disk 47″
across and shines brightly at magnitude
-2.7 from western Aquarius.
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
July interactions between Jupiter, 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.)
June 1: 5:24, 15:19; 2: 1:15, 11:11,
21:06; 3: 7:02, 16:58; 4: 2:53, 12:49,
22:45; 5: 8:40, 18:36; 6: 4:32, 14:27;
7: 0:23, 10:19, 20:14; 8: 6:10, 16:06; 9:
2:01, 11:57, 21:53; 10: 7:48, 17:44; 11:
3:39, 13:35, 23:31; 12: 9:26, 19:22; 13:
5:18, 15:13; 14: 1:09, 11:05, 21:00; 15:
6:56, 16:52; 16: 2:47, 12:43, 22:39; 17:
8:34, 18:30; 18: 4:25, 14:21; 19: 0:17,
10:12, 20:08; 20: 6:04, 15:59; 21: 1:55,
11:51, 21:46; 22: 7:42, 17:37; 23: 3:33,
13:29, 23:24; 24: 9:20, 19:16; 25: 5:11,
15:07; 26: 1:02, 10:58, 20:54; 27: 6:49,
16:45; 28: 2:41, 12:36, 22:32; 29: 8:27,
18:23; 30: 4:19, 14:14
July 1: 0:13, 10:09, 20:05; 2: 6:00,
15:56; 3: 1:51, 11:47, 21:43; 4: 7:38,
17:34; 5: 3:29, 13:25, 23:21; 6: 9:16,
19:12; 7: 5:07, 15:03; 8: 0:59, 10:54,
20:50; 9: 6:45, 16:41; 10: 2:37, 12:32,
22:28; 11: 8:24, 18:19; 12: 4:15, 14:10;
13: 0:06, 10:02, 19:57; 14: 5:53, 15:48;
15: 1:44, 11:40, 21:35; 16: 7:31, 17:26;
17: 3:22, 13:18, 23:13; 18: 9:09, 19:04;
19: 4:59, 14:56; 20: 0:51, 10:47, 20:42;
21: 6:38, 16:34; 22: 2:29, 12:25, 22:20;
Sky & Telescope - July 2021

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