Philips Atlas of the Universe

Eridanus(southern), Horologium, Caelum, Dorado, Reticulum,

E

ridanus, the River, stretches down into the far south,

ending at Achernar, which is the ninth brightest star in

the sky; it is 144 light-years away, and 1000 times as lumi-

nous as the Sun. It can be seen from anywhere south of

Cairo; from New Zealand it is circumpolar.

There is a minor mystery attached to Acamar, or ı

Eridani. Ptolemy ranked it as of the first magnitude, and

seems to have referred to it as ‘the last in the River’, but it

is now little brighter than magnitude 3. It is not likely to

have faded, and it is just possible that Ptolemy had heard

reports of Achernar, which is not visible from Alexandria

• though Acamar can be seen, low over the horizon.
  Acamar, 55 light-years away, is a splendid double, with
  one component rather brighter than the other; both are
  white, of type A, and are respectively 50 and 17 times
  more luminous than the Sun.
  Horologiumis one of Lacaille’s obscure constellations,
  bordering Eridanus. The only object of any note is the red
  Mira variable R Horologii, which can rise to magnitude
  4.7 at maximum. It is rather isolated, but ̄and ÊEridani,
  near Achernar, point more or less to it.
  Caelumis another Lacaille addition; he seems to have had
  a fondness for sculpture, since Caelum was originally
  Caela Sculptoris, the Sculptor’s Tools. There is nothing of
  interest here; the constellation borders Columba and
  Dorado.
  Dorado, the Swordfish, once commonly known as Xiphias.
  It lies between Achernar and Canopus. The most notable

star is ‚, which is a bright Cepheid variable; it has a period

of over 9 days, and is therefore considerably more lumi-

nous than ‰Cephei itself. If its distance is correctly given

in the Cambridge catalogue, it is 7500 light-years away,

with a peak luminosity 200,000 times that of the Sun.

Most of the Large Magellanic Cloud lies in Dorado,

and here we have the superb nebula 30 Doradûs, probably

the finest in the sky. The Large Cloud, 169,000 light-years

away, was once classed as an irregular galaxy, but shows

clear indications of barred spirality. It remains visible

with the naked eye even in moonlight, and is of unique

importance to astronomers – which is partly why so many

of the latest large telescopes have been sited in latitudes

from which the Cloud is accessible. There have been

various novae in it, and the spectacular supernova of 1987.

Reticulumwas originally Reticulus Rhomboidalis, the

Rhomboidal Net. It is a small but compact group bor-

dering Eridanus and Hydrus, not far from Achernar and

the Large Cloud. Of its leading stars, ‚(3.85), Á(4.51),

‰(4.56) and Â(4.44) are all orange, with K- or M-type

spectra, so that they are quite distinctive. The Mira vari-

able R Reticuli, with a magnitude range of from 6.5 to 14,

lies in the same wide field with ·, and when near maxi-

mum is a binocular object. Close beside it is R Doradûs,

just across the boundary of the Swordfish, which is a red

semi-regular star always within binocular range.

Hydrus, the Little Snake, is easy enough to find, though

it is far from striking. ·and ‚are relatively nearby stars;

ATLAS OF THE UNIVERSE

 The region of the south

celestial poleis decidedly

barren; if there is any mist,

for example, the whole

area of the sky will appear

completely blank, and even

against a dark sky the south

polar star, ÛOctantis, is

none too easy to identify.

The nearest reasonably

bright star to the pole is

‚Hydri, but the distance is

almost 13°. The polar area

is divided up into small

constellations, few of which

are easy to locate, but the

Large Cloud of Magellan is

present, mainly in Dorado

but extending into Mensa.

It is also worth noting that

Achernar lies fairly close

to ·Hydri.

 Large Magellanic Cloud

(left) and Small Magellanic

Cloud (right) are the nearest

notable galaxies: the LMC

is 169,000 light-years away,

the SMC slightly further.

Magnitudes

Variable star

Galaxy

Magellanic Cloud

Gaseous nebula

Globular cluster

Open cluster

–1

0 1 2 3 4 5

CAELUM

HOROLOGIUM

ERIDANUS

RETICULUM

PICTOR

DORADO

MENSA

HYDRUS

VOLANS

CARINA

MUSCA

APUS

OCTANS

TUCANA

Canopus

Achernar

Á

·

‰

ı

È

Î

Ê

̄

·

Ï · ̇ ‰ Á ‚

Â

‰

Á

·

‚

Á

·

‚

· ı

Á ‰

‚

Û

‰

‚

Ó

·

Á

‰ ‚

Ï

Á

‰

‚

·

Â

‚

Á

·

R

R

R

2070

PHOENIX

COLUMBA

4372

4833

ı R

„

‰

̇

Ë

ı

ˆ

‚

̆

Î È

·

‰

LMC

CHAMAELEON

Ë

Â

^2

̄^1

È

̄

·

Á

‚

‚

Â

VELA

TRIANGULUM

AUSTRALE

‰

Â

·

Gb Atl of Univ Phil'03stp 2/4/03 7:43 pm Page 260