Sky & Telescope - December 2023 - 57

Going Deep by Scott Harrington
IC 10 - The Hidden Dwarf
It may be small, but it's quite the treasure trove for owners of large telescopes.
LOCAL GEM IC 10, a likely satellite of the
Andromeda Galaxy, was the last member of
the Local Group discovered visually. The image
at left was obtained with the telescopes of Kitt
Peak National Observatory in Arizona.
an NGC designation. It garnered little
attention until 1935, when Nicholas
Mayall of Lick Observatory concluded
it was " extra-galactic. " He did so after
studying several photographs taken
using some of the largest telescopes of
the day. However, substantial foreground
extinction due to the object's location
just 3.3° below the galactic plane made
it difficult to classify any further.
The following year, Edwin Hubble
I
t's been almost a decade since I first
observed one of the largest, most massive
star-forming regions in our Local
Group of galaxies. The sight of it in my
vintage 10-inch Schmidt-Cassegrain
telescope (SCT) left me reeling. Despite
what you might be thinking, I hadn't
just observed the Great Orion Nebula.
What I saw was more a feast for the
imagination than the eyes, considering
it lies 2,000 times farther and yet is at
least 25 times larger.
I'm talking about NGC 604, a massive
emission nebula in the Triangulum
Galaxy (S&T: Nov. 2023, p. 58).
Ever since that observation, I've been
passionately (maybe even obsessively?)
seeking every type of deep-sky object
possible within galaxies outside our
own (S&T: May 2021, p. 22). I mean,
seeing a globular cluster in our Milky
Way is nice . . . but I think seeing one
in another galaxy is beyond marvelous.
And that's where the obscure galaxy
IC 10 comes in.
EAST OF BETA CASSIOPEIAE Look for tiny
IC 10 at RA = 00h 20.4m and Dec = +59° 18′.
Swift's Galaxy
Comet hunter Lewis Swift first chanced
upon IC 10, just 1.5° east of Beta (β)
Cassiopeiae, in October 1887 while he
was searching for new nebulae using a
16-inch Clark refractor from Rochester,
New York. However, he published his
finding a few months too late for John
Louis Emil Dreyer to include it in the
New General Catalogue of Nebulae and
Clusters of Stars, published in 1888, and
so this remarkable galaxy didn't receive
1h 30m
ε
CASSIOPEIA
δ
M103
3
2
4
5
6
7
θ
ζ
sk yand tele scope .o r g * DECEMBER 2023 57
γ
IC 10
η
α
+55°
κ
+60°
+60°
β
3
4
5
6
7
8
9
IC 10
β
1h 00m
0h 30m
+65°
published his seminal book The Realm of
the Nebulae. In it, he called IC 10 " one
of the most curious objects in the sky "
and noted it might be a possible member
of what he termed the " local group "
of galaxies . . . if its distance could be
determined. In 1941, Mayall obtained
radial velocities through spectroscopy
that not only proved IC 10 to be outside
our own galaxy but that its two brightest
" condensations " were not unlike
emission nebulae.
A Mystery for the Ages
Owing to IC 10's location and appearance,
Russian astronomers Grigory
0h 30m
0h 20m
0h 10m
+58°
KPNO / NOIRLAB / NSF / AURA; DATA OBTAINED AND PROCESSED BY: P. MASSEY (LOWELL OBS.) / G.
JACOBY, K. OLSEN, C. SMITH (NOAO / AURA / NSF); IMAGE PROCESSING: TRAVIS RECTOR (UNIVERSITY
OF ALASKA ANCHORAGE) / MAHDI ZAMANI / DAVIDE DE MARTIN
Star magnitudes
Star magnitudes

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Sky & Telescope - December 2023

Table of Contents for the Digital Edition of Sky & Telescope - December 2023