Sky and Telescope - January 2017 - 54

JANUARY 2017 OBSERVING
Sue
Deep-Sky Wonders by S
u French
ue

A River Full of Galaxies
Beneath Orion's foot Eridanus begins
His winding course, and reaches Cetus' fins.
- Aratus, Phaenomena, translated by
John Lamb 1848

A

Star magnitudes

cross the ages, the constellation
Eridanus, the River, has been portrayed with surprising variety. Arguably,
its most captivating depiction appears
in the beautiful edition of Phaenomena
published in 1600 by Hugo Grotius and
called Syntagma Arateorum. Its illustrations were inspired by an illuminated
manuscript Grotius possessed, and
their superb execution was carried out
by engraver Jacob de Gheyn. In turn,
b
p Dutch artist Jacob de Gheyn engraved this
de Gheyn's engraving style influenced
d
depiction of Eridanus for the 1600 edition of SynJohann
Bayer's magnificent pictorial
JJo
o
tagma Arateorum (Phaenomena) by Hugo Grotius.
atlas,
Uranometria.
In Syntagma Arateoa
rum,
a
starry
river-god
personifies Eridam
3h 40m
3h 35m
nus, his waters spilling from an urn and
20
swirling around him.
Although the river-god himself is
bedecked with stars, the further depths
-18°
of this swath of sky abound with the
1394 1391
IC 343
celestial behemoths known as galaxies.
1393
The all-sky chart at the center of this
1402
1407
magazine shows Eridanus in the more
1400
traditional form of a flowing river of
-19°
stars. The great oxbow bend in northern
Eridanus crosses the chart's meridian,
and within its embrace dwell a bevy of
galaxies within the grasp of modest,
ERIDANUS
backyard telescopes.
-20°
NGC 1407 is the brightest galaxy in
the river's bend, and we find it accompanied by an entourage of smaller
companions. Through my 130-mm
5
refractor and a wide-angle eyepiece giv6
-21°
7
ing 23×, NGC 1407 and the 5.2-mag8
nitude star 20 Eridani share the field of
9
τ5
view. This round galaxy is easily visible
10
and displays a sizable, moderately faint
halo encasing a small bright center.
54

J A N U A R Y 2 0 1 7 * SK Y & TELESCOPE

At 63× NGC 1400 emerges southwest
of NGC 1407 as a smaller version of
its neighbor. The larger galaxy spans
roughly 4′; NGC 1400 is about half that
diameter. A starlike nucleus resides at
the heart of each galaxy, but NGC 1407
boasts the more prominent one. At 117×
diminutive NGC 1393 joins the scene
like a small child running ahead of its
parents. The wee tyke is a bit difficult
to see, however, so use averted vision to
catch sight of it. The galaxies mark the
corners of a 20′-tall right triangle.
Through my 10-inch reflector at 90×,
NGC 1393 has an oval profile that's
tipped north-northwest and grows
brighter toward the center. Four little
scraps of fluff with assorted inclinations
surface in the field of view - NGC 1402,
IC 343, NGC 1391, and NGC 1394. At
118× IC 343 exposes a brighter core.
Although the galaxies look as though
they might be associated, they're actually sorted into two distinct groups.
NGC 1407, NGC 1400, NGC 1393, and
IC 343 belong to the NGC 1407 Group,
some 86 million light-years distant,
while the other galaxies are members of
a more remote group 185 million lightyears away from us.
Our next five galaxies are part of
another group at a distance of about
68 million light-years. It and the NGC
1407 Group are components of a larger
aggregation of about 200 galaxies,
sometimes called the Eridanus Cluster.
NGC 1300 is probably the most wellknown galaxy of the quintet because of
its prominent bar and the impressive
spiral arms that spring from each end.
A striking image composed of exposures
from the Hubble Space Telescope reveals
a spiral swirl at the center of the bar, a
feature only seen in galaxies with large

DR AWING: LINDA H A LL LIBR A RY OF SCIENCE, ENGINEERING & TECHNOLOGY

Plumb the galactic depths of Eridanus this month.



Sky and Telescope - January 2017

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

Contents
Sky and Telescope - January 2017 - Cover1
Sky and Telescope - January 2017 - Cover2
Sky and Telescope - January 2017 - 1
Sky and Telescope - January 2017 - Contents
Sky and Telescope - January 2017 - 3
Sky and Telescope - January 2017 - 4
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Sky and Telescope - January 2017 - Cover3
Sky and Telescope - January 2017 - Cover4
Sky and Telescope - January 2017 - SGA17RAL
Sky and Telescope - January 2017 - 90
Sky and Telescope - January 2017 - SGA17R
Sky and Telescope - January 2017 - SGA17RA
Sky and Telescope - January 2017 - SGA17EAL
Sky and Telescope - January 2017 - 94
Sky and Telescope - January 2017 - SGA17E
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Sky and Telescope - January 2017 - SGA17SAL
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Sky and Telescope - January 2017 - SGA17S
Sky and Telescope - January 2017 - SGA17SA
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