The story of the universe. Volume 1 (of 4) : $b The starry skies
History
The story of the universe. Volume 1 (of 4) : $b The starry skies
Astronomy; Earth (Planet); Natural history
When we look on the region of the celestial vault which surrounds
the South Pole, we can not help being struck with the contrast
presented by the small quantity of stars which it contains, with the
brilliant zone which borders the Milky Way, from Orion and Argo to
the Centaur, passing by the Southern Cross. One solitary star of the
first magnitude, Achernar, more distant from the pole than are the
beautiful stars of the Centaur and of the Cross, shines in this part
of the sky.
But even this circumstance renders the singular aspect of the two
nebulous spots, which seem two detached pieces of the great galactic
zone, still more striking. These half-stellar, half-nebulous systems,
unequal in magnitude and brightness, but easily seen with the naked
eye on a clear, moonless night, are situated, one, the larger and
more brilliant, between the pole and Canopus, in the constellation
of Doradus; the other, the smaller and less brilliant, ordinarily
visible during the full moon, in Hydrus, between Achernar and the
pole.
Both are known by astronomers and navigators under the name of “Cape
Clouds,” or again, “Magellanic Clouds.” And, to distinguish them, we
have again the Great Cloud (_Nebecula Major_) and the Small Cloud
(_Nebecula Minor_).
The Clouds of Magellan are distinguished from all other nebulæ by
their great apparent dimensions, and by their physical structure;
this last character distinguishes them from most of the branches and
offshoots of the Milky Way, with which, we may also add, they do not
appear connected in any way.
The Great Cloud extends over a space which embraces not less than
forty-two square degrees—about two hundred times the apparent surface
of the lunar disk. The Small Cloud occupies in extent four times less
than the other; according to Humboldt, it is surrounded “with a kind
of desert,” where, it is true, shines the magnificent stellar cluster
of Toucan. If the exterior aspect of these two remarkable nebulæ,
and their situation in a celestial region poor in stars, give to the
southern sky a peculiar appearance, their real structure makes them
one of the wonders of the heavens.
In the Great Cloud, Herschel has counted 582 single stars, among
which one only is of the fifth magnitude; six others are of the order
immediately inferior, and would doubtless be visible to the naked eye
if their light were not effaced by the general glare.
In the Small Cloud, the single stars are proportionally more
numerous, since 200 have been counted, among which three are of the
sixth magnitude, while it only includes thirty-seven of the nebulæ
and seven star-clusters. These immense aggregations, the elements of
which are themselves swarms of suns, remind us of the largest, in
appearance at least, of all the clusters which the eye contemplates
in the depths of the sky—the Milky Way.
Public-domain text, read in full here on John Shaqi.
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