Sky & Telescope - July 2024 - 56

JULY 2024 OBSERVING
Suburban Stargazer
42
17h 20m
+48°
6229
+46°
52
3
4
5
6
7
8
9
17h 10m
17h 00m
16h 50m
16h 40m
16h 30m
southwest. The guardians are handy
for re-focusing different eyepieces.
My patient use of averted vision and
magnifications between 93× and 108×
teases out 12th-magnitude flecks of
light across the cluster, turning it into a
grainy sphere. Not bad for a small scope.
The 10-inch does way better. At 48×,
+44°
M92
+42°
HERCULES
σ
M13 grows smoothly brighter from the
edge to the middle. An eyepiece yielding
64× resolves the surrounding halo into
stars; doubling to 128× adds numerous
pinpoints throughout the interior.
At 169× to 218×, the glittering sphere
displays irregular clumps of stars separated
by narrow voids. The patchy effect
becomes stronger with increased magnification.
And to my eye, several long
chains of stars curve southwestward, in
the general direction of the 7.3-magnitude
guardian.
Bonus time: Three double stars lie
+40°
η
+38°
ρ
+36°
cr
69
6207
π
Σ2101
Σ2104
M13
Σ2097
W
just southeast of M13. Struve (Σ) 2104
has 7.5- and 8.8-magnitude components
5.7″ apart. Less than 40′ west of
that duo is Σ2101, which offers 7.5- and
9.4-magnitude stars spanning 4.1″. Both
tandems resolve at around 100×. The
third binary, Σ2097, stands 14′ northwest
of Σ2101. This one is tough. The
9.4- and 9.6-magnitude components,
separated by only 1.9″, barely split in my
10-inch at 169×. The dim dots are too
tight for my smaller scope.
pGLOBULARS OF HERCULES M13 and M92 are both well-known globular star clusters, but try
also for NGC 6229, a diminutive globular in the northwestern part of the constellation. And don't
miss the three binary stars located just southeast of M13.
marked by 2.8-magnitude Zeta (ζ) at
the Keystone's southwest corner, and
3.5-magnitude Eta (η) Herculis on
the northwest corner. M13 is found
two-thirds of the way from Zeta to Eta.
Glowing at magnitude 5.8 and 20′ in
diameter, you should see the globular
readily in your finderscope.
M13 is a cosmic hive of several hundred
thousand ancient suns. Fabulous.
But our ability to resolve a globular into
stars depends on both the size of your
scope and the luminosity of the bright56
JULY 2024 * SKY & TELESCOPE
est cluster members. The leading lights
of M13 shine at magnitude 11.9, and
with good sky conditions, a 4-inch telescope
can detect stars down to magnitude
12.7. My sky conditions aren't even
close to good, but let's see what I can do.
In the 4¼-inch reflector at 27×, M13
is a diffuse sphere with a broad, bright
middle. As shown in the photo on page
55, the cluster is flanked by two guardians
- a 6.8-magnitude orange star 15′
to the east and a 7.3-magnitude white
star a similar distance to the southMidsize
Marvel
M13's less famous cousin lies almost
10° northeastward. M92 is w-a-a-a-y
up there. Observers near the latitude
of Denver, Colorado, can watch M92
climb to a point just north of the
zenith. From my home at around 49°
North, I have to crane my neck to sight
M13 - M92 is even worse!
Get ready for one big star-hop. M92
is located roughly two-thirds of the way
from Eta Herculis to 3.8-magnitude
Iota (ι), a lonely light in northeastern
Hercules. Eta and Iota are about 12°
apart - too widely spaced to fit in a
finderscope field. No problem. I place
Eta in my finder, then shift northeastward
until Iota swims into view. There's
no other star as bright as Iota to distract
me along the way. M92 is less than 5°
Star magnitudes

Sky & Telescope - July 2024

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