Cetus, Eridanus (northern), Fornax
C
etus is a vast constellation, covering 1232 square
degrees. Mythologically it is said to represent the sea-
monster which was sent to devour the Princess
Andromeda, but which was turned to stone when Perseus
showed it the Gorgon’s head.
The brightest star, ‚(Diphda), can be found by using
Alpheratz and ÁPegasi, in the Square, as pointers. It is an
orange K-type star, 68 light-years away and 75 times as
luminous as the Sun. It has been strongly suspected of
variability, and is worth monitoring with the naked eye,
though the lack of suitable comparison stars makes it
awkward to estimate. ıand Ëlie close together; ıis
white, and Ë, with a K-type spectrum, rather orange. In
the same binocular field there is a faint double star,
37 Ceti.
ÙCeti is of special interest. It is only 11.9 light-years
away and about one-third as luminous as the Sun, with a
K-type spectrum. It is one of the two nearest stars which
can be said to be at all like the Sun (ÂEridani is the other),
and it may be regarded as a promising candidate for the
centre of a planetary system, so that efforts have been
made to ‘listen out’ for signals from it which might be
interpreted as artificial – so far with a total lack of success.
The flare star UV Ceti lies less than three degrees south-
west of Ù.
The ‘head’ of Cetus is made up of ·, Á, Ì, Íand ‰.
·(Menkar) is an M-type giant, 130 light-years away and
132 times as luminous as the Sun; it too has been sus-
pected of slight variability. It is a binary with a very long
revolution period; it is fairly easy to split with a small
telescope.
Mira (ÔCeti) is the prototype long-period variable,
and has been known to exceed the second magnitude at
some maxima, though at others it barely rises above 4.
It is visible with the naked eye for only a few weeks every
year, but, when at its best, it alters the whole aspect of
that part of the sky. It was the first variable star to beidentified, and is also the closest of the M-type giants;
its distance is 420 light-years, and it is over 100 times as
powerful as the Sun. The average period is 331 days.
Mira’s diameter is around 680 million kilometres (425
million miles) but it swells and shrinks. It is a binary;
the companion, of around magnitude 10, is the flare star
VZ Ceti.
M77 is a massive Seyfert spiral galaxy, and is a strong
radio source. It lies near ‰, and is not hard to locate, but
its nucleus is so bright compared with the spiral arms
that with low or even moderate magnifications it takes on
the guise of a rather fuzzy star. The distance is about 52
million light-years. NGC247 (C62), close to ‚, is fairly
large, but has a low surface brightness, and is also placed
at an unfavourable angle to us, so that the spiral form is
not well displayed. All the other galaxies in Cetus are con-
siderably fainter.
Eridanus. Only the northern part of this immensely long
constellation is shown here; the rest sprawls down into the
far south of the sky. In mythology Eridanus represents the
River Po, into which the reckless youth Phaethon fell after
he had obtained permission to drive the Sun-chariot for
one day – with the result that the Earth was set on fire, and
Jupiter had to call a reluctant halt to the proceedings by
striking Phaethon with a thunderbolt.
There is not a great deal to see in the northern part of
the River. There are only two stars above the third mag-
nitude; ‚or Kursa, close to Rigel in Orion (type A, 96
light-years away, 83 times as luminous as the Sun) and Á
or Zaurak (type M, 114 light-years away, 120 Sun-
power). It is worth looking at the ‰–Âpair. ‰(Rana) is
fairly close, at a distance of 29 light-years, and is a
K-type star only 2.6 times as luminous as the Sun; next to
it is Â, at a distance of 10.7 light-years, which, with ÙCeti,
is one of the two nearest stars to bear any resemblance to
the Sun. The IRAS satellite found that it is associated
with cool material, and is known to be attended by oneATLAS OF THE UNIVERSE
The constellations
in this map are seen to
advantage during evenings
in late autumn (northern
hemisphere) or late spring
(southern). Cetus is large
but rather faint, though
the ‘head’, containing
·(Menkar) is not hard
to identify. Eridanus is so
immensely long that not
all of it can be conveniently
shown on one map; the
southern part is contained
in Star Map 22, the south
polar region – the ‘river’
ends with the brilliant
Achernar, which does
not rise from anywhere
north of Cairo. Lepus is
also shown here, but
is described with Orion.MagnitudesVariable starGalaxyPlanetary nebulaGaseous nebulaGlobular clusterOpen cluster–1
0 1 2 3 4 5TAURUS
ERIDANUS
CETUSFORNAX
PISCES
CAELUM
SCULPTOR
RigelMiraς
ˆÌÓ53‰ÂËÁ6(^54)
1
3
1
2
54
Ù
Ù Ù
Ù
Ù
̆
̆
̆^3
41
ı È
·
Ó
‚
Í ̇
·
Á
Ó
Ì
‰ 75
̇
Ù
ı
Ë
È
‚
̆
g
f
S
Ù R
247 T
1398
1291
M77
ÔÁÂ̇‰
ËÔ^1
Ô^2‚Â ‰
ÓÔ·Â ÔLEPUS
Í
Ì Ô
Ó·Ì‚
Â̄Gb Atl of Univ Phil'03stp 2/4/03 7:42 pm Page 246