One of the wonders which most attracted the attention of early
explorers in the southern hemisphere, and roused as much interest as
the Southern Cross, was the pair of faint clouds, looking like detached
pieces of the Milky Way, which are seen in the neighbourhood of the
South Pole. Marco Polo made a sketch of the Greater Cloud, which he
describes wonderingly as “a star as big as a sack.”
Although some star-maps show short branches of Milky Way pointing
towards the two Clouds, this is incorrect, and they are quite separate
from it. Herschel was struck by their isolation, especially in the
case of the Little Cloud, which he described as situated in a “most
oppressively desolate desert,” its only neighbour being the globular
cluster 47 Toucani, which is near, but separated by a perfectly black
sky.
The Greater Cloud is much brighter to the naked eye than the Lesser,
and it is much more complex and interesting in the telescope. It
contains, moreover, the wonderful Looped Nebula, of which we have
already spoken.
Both Clouds consist of gaseous nebulae and star-clusters on a
background of vague nebulosity and crowds of almost indistinguishable
stars. But the white nebulae shun the Clouds, just as they shun the
Milky Way.
An immense number of variable stars have been discovered in the Clouds
of Magellan, of the same type as those in globular clusters. Miss
Leavitt of Harvard Observatory catalogued from photographs no less
than 969 in the Lesser Cloud and 800 in the Greater. In the latter
the greatest number of variables was found in a stream of faint stars
which connects a group of star-clusters with the Looped Nebula, and
others occur locally in certain parts of the Cloud, but few are in
its northern region or in parts where many of the brighter stars
congregate. All the variables are very faint, the usual minimum in both
Clouds being about fourteenth magnitude, and the maximum seldom more
than one magnitude brighter. A few in the Lesser Cloud have been found
with periods unusually long for this “cluster type” of variables,
amounting to 32, 66, and even 127 days. These longer periods seem to
belong to somewhat brighter stars, but they are quite as exact as the
usual period of a few days or a single day.