Capricornus, Aquarius, Piscis Australis
C
apricornushas been identified with the demigod Pan,
but the mythological association is decidedly nebulous,
and the pattern of stars certainly does not recall the shape
of a goat, marine or otherwise. Neither can it be said that
there is a great deal of interest here, even though the con-
stellation covers over 400 square degrees of the sky. ‰is
the only star above the third magnitude; it is about 49
light-years away, and some 13 times as luminous as our
own Sun.
‚Capricorni is one of the less powerful of the naked-
eye stars, and is not much more than twice the luminosity
of the Sun, though its distance is not known with any
certainty and may be less than the official value given
in the Cambridge catalogue. It has a sixth-magnitude
companion which is within binocular range and is itself a
very close double. The bright star appears to be a spectro-
scopic triple, so that ‚Capricorni is a very complex
system indeed.
·^1 and ·^2 make up a wide pair, easily separable with
the naked eye, but there is no genuine association. The
brighter star, ·^2 , is 117 light-years away, while the fainter
component, ·^1 , is very much in the background at a
distance of 1600 light-years; both are of type G, but
while the more remote star is well over 5000 times as
powerful as the Sun, the closer member of the pair could
equal no more than 75 Suns. This is a classic example of
an optical pair.
There are no notable variables in Capricornus, but
there is one Messier object, the globular cluster M30,
which lies close to ̇(which is, incidentally, a very lumi-
nous G-type giant). M30 was discovered by Messier
himself in 1764, and described as ‘round; contains no
star’. It is in fact a small globular with a brightish nucleus;
it is 41,000 light-years away, and has no characteristics of
special note.
Aquarius, with an area of almost a thousand square
degrees, is larger than Capricornus, but it is not a greatdeal more conspicuous. It is known as the Water-bearer,
but its mythological associations are vague, though it has
sometimes been identified with Ganymede, the cup-bearer
to the Olympian gods. Its main claim to fame is that it lies
in the Zodiac. Most of it is in the southern hemisphere of
the sky.
Both ·and ‚are very luminous and remote G-type
giants. The most interesting star is ̇, which is a fine binary
with almost equal components; both are F-type subgiants
about 100 light-years away, with a real separation of at
least 15,000 million kilometres (over 9000 million miles).
This is an excellent test object for a telescope of around
7.6-centimetre (3-inch) aperture.
There is a distinctive group of stars between
Fomalhaut, in Piscis Australis, and ·Pegasi. The three
stars labelled ‘„Aquarii’ are close together, with ̄and Ê
nearby; several of them are orange, and they have often
been mistaken for a very loose cluster, though they are not
really associated with each other.
R Aquarii is a symbiotic or Z Andromedae type
variable. It is made up of a cool red giant together with
a hot subdwarf – both of which seem to be intrinsically
variable. The whole system is enveloped in nebulosity,
and the smaller star seems to be pulling material away
from its larger, less dense companion. R Aquarii is none
too easy to locate, but users of larger telescopes will find
that it repays study.
M2 is a particularly fine globular cluster, forming a
triangle with ·and ‚Aquarii. Some people claim that
they can see it with the naked eye; with binoculars it is
easy. It was discovered by Maraldi as long ago as 1746,
and is very remote, at around 55,000 light-years. Its centre
is not so condensed as with most globulars, and the edges
are not hard to resolve.
M72 is another globular, discovered by Méchain in
1780; it is 62,000 light-years away, and comparatively
‘loose’. It is one of the fainter objects in Messier’s list, andATLAS OF THE UNIVERSE
The two Zodiacal
constellations of Capricornus
and Aquarius occupy a wide
area, but contain little of
immediate interest, and
together with Pisces and
Cetus they give this whole
region a decidedly barren
look. Fomalhaut, in Piscis
Australis, is the southern-
most of the first-magnitude
stars to be visible from the
British Isles or the northern
United States; northern
observers, who never see
it high up, do not always
appreciate how bright it
really is. The celestial
equator just passes through
the northernmost part of
Aquarius.MagnitudesVariable starGalaxyPlanetary nebulaGaseous nebulaGlobular clusterOpen cluster–1
0 1 2 3 4 5PISCES
AQUARIUS CAPRICORNUS
PISCIS AUSTRALIS
AQUILA
MICROSCOPIUM
Â
·
‰ Á ‚Ù
Ì
ȉ ÁÈ ı
Â
36
̇
24ˆ
„
‚
·
1
2 ·Ë
̇ Á
·
‚
Ï ıÊ
̄
„ „Ù È
‰(^21)
ˆ^2 ˆ^1
2
98
(^9988)
Fomalhaut
Altair
R
M30
7009 M72
M2
SCULPTOR
GRUS
NGC 7293
 ‰
ˆ
È
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Ï Îı‚ËÁ
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̇Gb Atl of Univ Phil'03stp 2/4/03 7:42 pm Page 244