Sky & Telescope - August 2024 - 43

AQUILA
OPHIUCHUS
IC 4665
66
73
74
70
68
Cr 359
67
γ
β
SERPENS
CAUDA
Binocular Highlight by Mathew Wedel
Drifting Apart
A
Zenith
M14
stronomy often involves seeing things before
we understand them. We saw the stars before
we knew they were other suns, spiral nebulae before
we knew they were galaxies, and quasars before we
knew they were active galactic nuclei.
So too with this month's target, the probable open
+20°
cluster Collinder 359, also cataloged as Melotte 186.
Just as professional astronomers have, we'll
approach it through successive approximation. Start
with Gamma (γ) Ophiuchi, on the eastern shoulder of
Ophiuchus, the Serpent Bearer. Look for a brighter
glow resembling a fat tadpole extending about 8°
east to 74 Ophiuchi at the tail. Within that span, you'll
see a concentration in the diffuse glow of the Milky
Way, spangled with 4th- to 6th-magnitude stars.
The most famous grouping here is the acute tri0°
η
-20°
WHEN
TO
USE THE MAP
Late June 1 a.m.*
Early July Midnight*
Late July
11 p.m.*
8h
g Sou
Early Aug 10 p.m.*
Late Aug Dusk
*Daylight-saving time
angle formed by 66, 67, 68, 70, and 73 Ophiuchi. This
miniature mimic of the Hyades in the constellation
Taurus, the Bull, was part of the now-defunct constellation
Taurus Poniatovii (S&T: Aug. 2022, p. 20), and it
remains a charming asterism for binocular observers.
I use 7×50s to provide some context around Cr 359,
but 10×50s show more stars. A roughly 4°-wide circle
centered on 67 Ophiuchi - itself a nice binocular
double - marks the western boundary of the cluster.
Cr 359 is similar in distance and proper motion to
the nearby open cluster IC 4665, 4.5° northwest of
67 Ophiuchi. The two clusters may have interacted
early on, but over millions of years IC 4665 has held
together, while the stars of Cr 359 have started to
drift apart - the eventual fate of all open clusters.
Comparing the two allows us the heady experience
of witnessing galactic evolution firsthand.
¢ MATT WEDEL wonders about all the open clusters
that dissipated before he could observe them, while
keeping quite busy with the ones that are still around.
sk yand tele scope .o r g * AUGUST 2024 43
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S E R P E N S
( C A P U T )
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S C O R P I U S
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M8
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M19
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M62
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COMA
BERENICES
β
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CANES
VENATICI
L E O
M I N O R
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M A J O R
Mizar
& Alcor
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