58 AUSTRALIAN SKY & TELESCOPE November | December 2017
m 3 h 40 m 3 h 35 m–18°–19°–20°–21°1393
1402IC 343(^13941391)
τ^5
20
1400
1407
ERIDANUS
Star magnitudes
6
5
7
8
9
10
SDutch artist Jacob de Gheyn engraved this
depiction of Eridanus for the 1600 edition of
Syntagma Arateorum (Phaenomena) by Hugo
Grotius.
TARGETS by Sue French
A river full of galaxies
Plumb the galactic depths of Eridanus this summer.
Beneath Orion’s foot Eridanus begins
His winding course, and reaches Cetus’ fins.
— Aratus, Phaenomena, translated by
John Lamb 1848
ACROSS 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, de Gheyn’s engraving
style influenced Johann Bayer’s
magnificent pictorial atlas, Uranometria.
In Syntagma Arateorum, a starry river-god
personifies Eridanus, his waters spilling
from an urn and swirling around him.
Although the river god himself is
bedecked with stars, the further depths
of this swath of sky abound with the
celestial behemoths known as galaxies.
The all-sky chart at the centre of this
magazine shows Eridanus in the more
traditional form of a flowing river of
stars. Within the great oxbow bend
in northern Eridanus, dwell a bevy of
galaxies within the grasp of modest,
backyard telescopes.
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 refractor and a wide-angle
eyepiece giving 23=, NGC 1407 and
the 5.2-magnitude star 20 Eridani
share the field of view. This round
galaxy is easily visible and displays a
sizable, moderately faint halo encasing
a small bright centre. At 63=NGC 1400
emerges southwest of NGC 1407 as a
smaller version of its neighbour. The
larger galaxy spans roughly 4v; 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 20v-tall right triangle.
Through my 25-cm reflector at 90=,
NGC 1393 has an oval profile that’s
tipped north-northwest and grows
brighter toward the centre. 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 light-
years 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 well-
known 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 DRAWING: LINDA HALL LIBRARY OF SCIENCE, ENGINEERING & TECHNOLOGY