Sky & Telescope - July 2019 - 57

Going Deep by Richard P. Wilds

N

Rho Oph

The Nebulae
of Ophiuchus

Antares

Visit the Serpent Holder to snare a
collection of dark and bright nebulae
with just a few sweeps of your scope.

BA BA K TA FRESHI

T

he region of the sky in and around
Ophiuchus fascinated William
Herschel; E. E. Barnard repeatedly
returned to it in an attempt to understand the structure of the Milky Way. If
you spend a little time with the constellation, then you'll begin to understand
some of the historical misunderstandings that arose here. Observing this
region, Herschel reacted with shock as
he swept past such objects as the globular star clusters M80 and M4 only to
enter what would become known as the
dark nebula Barnard 42 and the bright
nebulae IC 4603 and IC 4604. He proclaimed that he'd discovered a "hole"
in the sky without a star to be seen.
William's sister, Caroline, wrote to her
nephew, John, warning him to take
care when observing this region - her
brother thought it might contain clues
to the understanding of the entire heavens. Indeed, until the 20th century the
Herschel family and the majority of the

scientiﬁc community held to the theory
that Herschel's "holes" came about
during the formation of the nearby
globular clusters. The theory proposed
that somehow stars in regions such as
Ophiuchus had been gathered up into
these wonderfully beautiful globular
star clusters, leaving only "vacancies"
to be viewed and pondered.
In fact, Herschel's conclusions were
the beginning of Barnard's journey
toward realizing that what he was
observing weren't "vacancies" at all,
but were bright and dark nebulae that
ﬁlled the area, much like in other parts
of the Milky Way. It would be left to
others in the early decades of the 20th
century to show that rather than globular star clusters forming by gathering
large numbers of stars out of "vacancies," it was the dark nebulae (and
other sources of absorbing dust) that
had the effect of hiding the globular
clusters from our view.

p THE GREAT NEBULA OF RHO OPHIUCHI
A cornucopia of celestial objects appears in
this image. Nebulae, both bright (IC 4603 and
IC 4604) and dark (Barnard 44), multiple-star
systems (Rho Ophiuchi itself), and globular
clusters (the most prominent being M4) all
contribute to the wonders of this particular
region of sky.

M80 and M4 are just over the border
in Scorpius, but Barnard 42, IC 4603,
and IC 4604 are solidly in Ophiuchus.
The three objects make for a wondrous
sight, worthy of a location in the sky
where scientiﬁc history would be repeatedly made in order to understand the
universe. Barnard made this threesome
famous, calling them collectively the
Great Nebula of Rho Ophiuchi. Just a
little more than 3° north-northeast of
Antares, the heart of the Scorpion, you
will slew into the darkness of B42 - this
dark nebula will dominate your view. A
little less than 1° south of Rho Ophiuchi, you'll ﬁnd IC 4603 surrounding the
s k y a n d t e l e s c o p e . c o m * J U LY 2 0 1 9

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