When we speak of the southern constellations, everyone thinks of the
Southern Cross, and every traveller coming south for the first time
is eager to see it. Some are disappointed because it is small and
irregular, but it is very brilliant, and lies in an extremely rich
region of the Milky Way. Very beautiful, too, is the way in which it is
seen rising on its side and gradually becoming upright as it reaches
its greatest height above the horizon, then sloping again as it glides
westward.
The Cross seems to have been first so named by the Spanish explorer
Amerigo Vespucci, at the beginning of the sixteenth century, and it
was also described in letters by the Florentine Andrea Corsali, who
says it is so beautiful that in his opinion no other constellation in
the sky is worthy to be compared with it. Some think, however, that
the stars had already been recognised as forming a Cross as early as
the thirteenth century, because Dante in his _Purgatory_ speaks of
four stars which glorified the southern sky; but he does not say they
were in the form of a cross, and he tells us that they had never been
seen before by mortal man except by our first parents, whose original
dwelling-place he sets in the southern hemisphere. This negatives the
suggestion that some traveller had described them to him.
About the same time as the Cross, other groups were named by sailors
and travellers in the part of the sky round about the south pole,
for this region had been left a blank by the framers of the ancient
constellations, doubtless because they lived too far north to see it.
Some students of astronomy in the Middle Ages concluded that there
really were no stars in this part, and Ristoro of Arezzo gravely argued
that this proved the absence of any land further south than India and
Ethiopia; for where there are no stars to pour down influences on the
earth no animals can live, and therefore no vegetation is needed for
their food, and no land for it to grow on.
The new constellations were mostly named after strange birds and fishes
seen by explorers in their southern voyages, and they were admitted to
scientific astronomy by Bayer, who made a map of the skies in 1604.
He also introduced the plan of naming each star in a constellation
by a Greek letter, the brightest of each constellation usually being
called Alpha, the next brightest Beta, and so on. One of these
constellations is Grus, the Crane (originally called the Flamingo), and
it is convenient to be familiar with it, because from it we may easily
identify several others. The chief stars of Grus form a striking curve
with a bright star close beside it. This bright star is Alpha Gruis,
and the brightest in the curve is Beta. A line through Alpha and Beta
leads in one direction to the brightest star of the Phoenix, in the
other direction to the brightest of the Indian; a line through Alpha
and the little naked-eye double Delta takes one to Pavo, the Peacock;
a line through Gamma (at one end of the curve) and Alpha goes to the
brightest star in the Toucan. And these are all the modern groups
containing bright stars except the Southern Triangle, near the Pointers
to the Cross (see p. 6), and Columba, the Dove, not far from Sirius,
each of which has one star brighter than third magnitude.[2] We may,
however, also notice Alpha Hydri, the brightest star in the small
Water-Snake, close to the bright star Achernar, and Alpha Doradūs, the
brightest of the Sword-Fish, between Canopus and Achernar.
[2] Stars are classified by astronomers in “magnitudes,” _i.e._ degrees
of brightness, those of first magnitude being the brightest. Stars
below sixth magnitude cannot be seen with the naked eye.
In the eighteenth century the French astronomer Lacaille, who did much
excellent work in the southern hemisphere with a tiny telescope of only
half an inch aperture, had the unhappy idea of filling up the spaces
still left empty with scientific instruments. It is easy to make Birds
of Paradise and Flying Fishes out of the stars, but such things as
telescopes, easels, and sextants do not lend themselves to irregular
groups, and they are very much out of place among the mythical beasts
and heroes which we are accustomed to see on our star-maps. Fortunately
the beginner need not learn to recognise these intruders, for there
are no bright stars in them, although there are many interesting
objects for telescopic study. We need only note that Octans, the
Octant, occupies the region in which the south pole is situated, which
is quite bare of bright stars. The pole itself may be found by drawing
a line from head to foot of the Cross and carrying it on about four
times as far again; or if the Cross is invisible, the pole may be found
near the middle of a line from Canopus to Alpha Pavonis.