Sky and Telescope - November 2017 - 58

NOVEMBER 2017 OBSERVING
Going Deep by Ken Hewitt-White

A Whale of a Galaxy Cluster
Reel in the denizens of Abell 194 - if those autumn skies ever clear.

1h 30m

1h 28m

1h 26m

1h 24m

1h 22m

HD 8779

1h 20m

1h 18m

43
42

CETUS

548

PGC 73958

PGC 5307
557

538

535

Abell 194
530
PGC 5164

IC 120
HD 8943

58

564
560
558
IC 119

PGC
5145

N O V E M B E R 2 0 17 * S K Y & T E L E S C O P E

-1°
Star magnitudes

HD 8578

6
7
8
9
10

-2°

then another ½° into Abell 194. There,
two elliptical galaxies, 4½′ apart and
slanted northeast-southwest, await us.

Arps at the Core
The more northerly object is actually
two galaxies: NGC 545 and NGC 547.
This binary blob comprises Arp 308, one
of 338 "peculiar" galaxies cataloged in
1966 by Palomar astronomer Halton C.
Arp (https://is.gd/ArpCatalog). Both
components of Arp 308 glow at magnitude 12.2, but NGC 545 is larger than
NGC 547. According to my records,
"the disc of NGC 545 is slightly elongated; the partner smaller and round.
Their bright cores seem roughly equal in
size and luminosity." Even at high magniﬁcation, the eye-catching pair struck
me as "two barely separate masses
enveloped in a single, broad halo."
Just 4½′ southwest of Arp 308 is
12.1-magnitude NGC 541. To my eye,
this spherical puffball seemed "larger,
more diffuse, a bit dimmer than either
part of Arp 308." But wait, there's more:
In their superb Arp Atlas of Peculiar
Galaxies, Jeff Kanipe and Dennis Webb
identify NGC 541 as Arp 133, an E0 (or
S0) galaxy with three "fragments" dotting its eastern edge. Chief among them
is Minkowski's Object, which they
describe as "a distorted magnitude-16.1
galaxy, apparently pushed to starburst
by a jet emerging from a black hole
in NGC 541." This miniscule outlier
escaped my scrutiny, but those with
larger light-buckets might succeed.

CE TI: HE V ELIUS

I

hope the following overview, drawn
from my observing log after impressions
voice-recorded at the eyepiece, will convince you that Abell 194 is worth more
than a single visit.
Most of our study area falls within
a narrow, northeast-leaning swath of
sky roughly 40′ long. The cluster's few
prominent members are clumped near
the northeast end, so let's begin there.
To star-hop to that spot, ﬁrst locate
3.6-magnitude Theta (θ) Ceti, then
shift 7¾° northward to 6.5-magnitude
43 Ceti. Don't confuse that star with
5.8-magnitude 42 Ceti to the west or
6.4-magnitude HD 8779 to the east.
Together the three dots form a 12/3°-long
row easily sighted in finderscopes. From
the middle star (43 Ceti), drop southeast 3/4° to 7.6-magnitude HD 8578,

had to chuckle at last May's Going
Deep column, which concluded by
saying that the author, Howard Banich,
"lives under the cloudy skies of western
Oregon." Boy, can I relate to that! At my
home in southwestern British Columbia, the November-through-March
period is one long, soggy season. As
with Howard's spring galaxies, my fall
fuzzies are "a rare treat."
A case in point is the galaxy cluster
Abell 194 in Cetus, which I haven't
revisited since I ﬁrst explored it ﬁve
autumns ago. My treatment here is the
product of one 90-minute observation,
during which I netted 18 cluster members (plus a few extras) with a 17.5-inch
f/4.5 Dobsonian working at 222× and
285× (amid excellent sky transparency,
but only moderately steady seeing). I
https://www.is.gd/ArpCatalog
Sky and Telescope - November 2017

Table of Contents for the Digital Edition of Sky and Telescope - November 2017
