Centaurus, Crux Australis,Triangulum Australe,
C
entauruswas one of Ptolemy’s original 48 groups.
·and ‚are the Pointers to the Southern Cross; ·, the
brightest star in the sky apart from Sirius and Canopus,
has been known as Toliman, Rigel Kentaurus and Rigel
Kent, but astronomers refer to it simply as ·Centauri. It is
the nearest of the bright stars, and only slightly further
away than its dim red dwarf companion Proxima, which is
only of the 11th magnitude and is difficult to identify; it
lies two degrees from ·, and is a feeble flare star.
·itself is a magnificent binary, with components of
magnitudes 0.0 and 1.2. The primary is a G-type yellow
star rather more luminous than the Sun; the K-type second-
ary is the larger of the two, but has less than half the Sun’s
luminosity. The revolution period is 80 years. The appar-
ent separation ranges from 2 to 22 seconds of arc, so that
the pair is easy to resolve with a small telescope.
‚, known as Agena or Hadar, is a B-type star, 530
light-years away and 13,000 times the luminosity of the
Sun. Áis a binary with almost equal components, but
the separation is less than 1.5 seconds of arc, so that at
least a 10-centimetre (4-inch) telescope is needed to
resolve it. The Mira variable R Centauri lies between ·
and ‚. At its best it reaches naked-eye visibility.
ˆCentauri is much the finest globular cluster in the
sky. To the naked eye, it is a hazy patch in line with
Agena and second-magnitude ÂCentauri. It is one of the
nearer globulars at around 17,000 light-years. It probably
contains over a million stars, concentrated near the centre
of the system within no more than a tenth of a light-year.
There are several bright open clusters in Centaurus,
notably the two near Ï. There is also a remarkable galaxy,
NGC5128 (C77), which is crossed by a dark dust-lane, and
is a fairly easy telescopic object. In 1986 a bright supernova
was discovered in it by an Australian amateur astronomer,
Robert Evans, using his 32-centimetre (13-inch) reflector.
Crux Australis. There can be few people who cannot iden-
tify the Southern Cross, though it was not accepted as aseparate constellation until 1679. One of the four stars, ‰, is
more than a magnitude fainter than the rest, which rather
spoils the symmetry; neither is there a central star to make
an X, as with Cygnus in the far north. ·, ‚and ‰are hot and
bluish-white, while Áis a red giant of type M. ·(Acrux) is
a wide double, and there is a third star in the same telescop-
ic field. ‚,of type B, is slightly variable.
Triangulum Australe. The three leaders, ·, ‚and Á, form
a triangle; ·is identifiable because of its orange-red hue.
It is 55 light-years away, and 96 times as luminous as the
Sun. The globular cluster NGC6025 lies near ‚and is not
far below naked-eye visibility; binoculars show it well.
Circinuswas one of Lacaille’s additions, lying between
the Pointers and Triangulum Australe. ·is a wide double;
Áis a close binary.
Aralies between ıScorpii and ·Trianguli Australis.
Three of its leading stars, ‚, ̇and Ë, are orange K-type
giants; R Arae, in the same binocular field with ̇and Ë,
is an Algol-type eclipsing binary which never becomes
as faint as the seventh magnitude. Ara contains several
brightish clusters, of which the most notable is the globu-
lar NGC6397 (C86), close to the ‚–Ápair. It seems to be
no more than 8200 light-years away – probably the closest
globular cluster. NGC6352 (C81), near ·, is considerably
brighter even though it is further away.
Telescopiumis a small, dim constellation near Ara. The
only object of note is the variable RR Telescopii, less than
four degrees from ·Pavonis. It is very faint indeed, but
has flared up to the seventh magnitude.
Normais another obscure constellation formed by Lacaille,
and once known as Quadra Euclidis, or Euclid’s Quadrant.
It adjoins Ara and Lupus, and contains two fairly bright
open clusters; NGC6067, not far from Á, and the adjacent
NGC6087 (C89), round the Cepheid variable S Normae.
Lupusis an original constellation. It contains a number of
brightish stars, though there is no well-marked pattern.
NGC5722, close to ̇, is an open cluster within binocularATLAS OF THE UNIVERSE
The Southern Cross,
Crux Australis, is the
smallest constellation in
the sky, but one of the most
conspicuous, even if it is
shaped more like a kite than
an X. It is almost surrounded
by Centaurus, and the
brilliant Pointers, ·and ‚
Centauri, show the way to
it. Most of Centaurus is too
far south to be seen from
Europe; from New Zealand,
Crux is circumpolar. It is
highest during evenings in
southern autumn. Centaurus
is an imposing constellation;
it contains the finest of all
globular clusters, ˆCentauri.SOUTHERN CROSS
The distances and luminosities
of the four main stars in
Crux Australis:
Distance, Luminosity,
light-years Sun 1
· 360 3200–2000
‚ 460 8200
Á 88 160
‰ 260 1300LUPUS
ARA
NORMA
TRIANGULUM
AUSTRALECIRCINUS
CENTAURUS
CRUX
TELESCOPIUM MUSCA CARINA
SCORPIUS
AntaresAgenaAcruxJewel
Box̄ „ Êı
ËÁ
ˆ‰ ΂
Ï
·Ì Î̇ÚÙ
ÈÈ ı„
̄ ÓÈË
Ê Ì
̆
̆
̇ ˆÂ‚
·ÁÙ Û ‰ Ú ÏÌ Á‚ ‰·‚
Á·
‰ ‚ Â
Á·Â
·ı‚ Á‰̇
Ë·
̇Á1
22b
d
nfRRST5460
5139
5286
3766
6025
6362
6193
6397
6352
GG5822
5128
R6067
(^6087) Â
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Â
‰
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· Ú
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· Â Ï
ˆ ̆
HYDRA
LIBRA
RR
1 2
Í
Î
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Î
Magnitudes
Variable star
Galaxy
Planetary nebula
Gaseous nebula
Globular cluster
Open cluster
–1
0 1 2 3 4 5
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