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Page 61
[Illustration: Fig. 76.--Sprayed Cluster below ae in Hercules.]
[Illustration: Fig. 77.--Globular Cluster.]
In various parts of the heavens there are small globular well-defined
clusters, and clusters very irregular in form, marked with sprays
of stars. There is a cluster of this latter class in Hercules,
just under the S, in Fig. 72. "Probably no one ever saw it with a
good telescope without a shout of wonder." Here is a cluster of the
former class represented in Fig. 77. "The noble globular cluster,
o Centauri is beyond all comparison the richest and largest object
of the kind in the heavens. Its stars are literally innumerable;
and as their total light, when received by the naked eye, affects
it hardly more than a star of the fifth to fourth
[Page 217]
magnitude, the minuteness of each star may be imagined."
There are two possibilities of thought concerning these clusters.
Either that they belong to our stellar system, and hence the stars
must be small and young, or they are another universe of millions
of suns, so far way that the inconceivable distances between the
stars are shrunken to a hand's-breadth, and their unbearable splendor
of innumerable suns can only make a gray haze at the distance at
which we behold them. The latter is the older and grander thought;
the former the newer and better substantiated.
_Nebul�._
The gorgeous clusters we have been considering appear to the eye
or the small telescope as little cloudlets of hazy light. One after
another were resolved into stars; and the natural conclusion was,
that all would yield and reveal themselves to be clustered suns,
when we had telescopes of sufficient power. But the spectroscope,
seeing not merely form but substance also, shows that some of them
are not stars in any sense, but masses of glowing gas. Two of these
nebul� are visible to the naked eye: one in Andromeda (see Fig.
68), and one around the middle star of the sword of Orion, shown
in Fig.78. A three-inch telescope resolves th Orionis into the
famous trapezium, and a nine-inch instrument sees two stars more.
The shape of the nebula is changeable, and is hardly suggestive of
the moulding influence of gravitation. It is probably composed of
glowing nitrogen and hydrogen gases. Nebul� are of all conceivable
shapes--circular, annular, oval, lenticular, [Page 218] conical,
spiral, snake-like, looped, and nameless. Compare the sprays of the
Crab nebul� above z Tauri, seen in Fig. 79, and the ring nebula,
Fig. 80. This last possibly consists of stars, and is situated, as
shown in Fig. 81, midway between b and g Lyr�.
[Illustration: Fig. 78.--The great Nebula about the multiple Star
th Orionis. (See Frontispiece.)]
When Herschel was sweeping the heavens with his telescope, and
saw but few stars, he often said to his assistant, "Prepare to
write; the nebul� are coming." They are most abundant where the
stars are least so. A zone about the heavens 30� wide, with the
Milky Way in the centre, would include one-fourth of the celestial
sphere; but instead of one-fourth, we find nine-tenths
[Page 219]
of the stars in this zone, and but one-tenth of the nebul�.
These immense masses of unorganized matter are noticed to change
their forms, vary their light greatly, but not quickly; they change
through the ages. "God works slowly." He takes a thousand years
to lift his hand off.
[Illustration: Fig. 79.--Crab Nebula, near z Tauri. (See Frontispiece.)]
There are many unsolved problems connected with these strange bodies.
Whether they belong to our system, or are beyond it, is not settled;
the weight of evidence leans to the first view.
[Page 220]
_Variable Stars._
[Illustration: Fig. 80.--The Ring Nebula.]
Our sun gives a variable amount of light, changing through a period
of eleven years. Probably every star, if examined by methods
sufficiently delicate and exact, would be found to be variable.
The variations of some [Page 221] stars are so marked as to
challenge investigation. b Lyr� (Fig. 81) has two maxima and minima
of light. In three days it rises from magnitude 4-1/2 to 3-1/2; in a
week falls to 4, and rises to 3-1/2; and in three days more drops to
4-1/2: it makes all these changes in thirteen days; but this period
is constantly increasing. The variations of one hundred and
forty-three stars have been well ascertained.
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