nsifies scintillation, and this is
usually regarded as a prognostication of rain. White stars twinkle more
than red ones. The occurrence of scintillation can be accounted for by
the fact that the stars are visible as single points of light which
twinkle as a whole, but in the case of the Sun, Moon, and planets, they
form discs from which many points of light are emitted; they,
therefore, do not scintillate as a whole, for the absence of rays of
light from one portion of their surface is compensated by those from
other parts of their discs, giving a mean average which creates a
steadiness of vision.

The stars are divided into separate classes called 'magnitudes,' by
which their relative apparent size and degree of brightness are
distinguished. The magnitude of a star does not indicate its mass or
dimensions, but its light-giving power, which depends partly upon its
size and distance, though mainly upon the intensity of its luminosity.
The most conspicuous are termed stars of the first magnitude; there are
ten of those in the Northern Hemisphere, and an equal number south of
the equator, but they are not all of the same brilliancy. Sirius
outshines every other star of the firmament, and Arcturus has no rival
in the northern heavens. The names of the first-magnitude stars north of
the equator are: Arcturus, Capella, Vega, Betelgeux, Procyon, Aldebaran,
Altair, Pollux, Regulus, and Deneb. The next class in order of
brightness are called second-magnitude stars; they are fifty or sixty in
number, the most important of which is the Pole Star. The stars diminish
in luminosity by successive gradations, and when they sink to the sixth
magnitude reach the utmost limit at which they appear visible to the
naked eye. In great telescopes this classification is carried so low as
to include stars of the eighteenth and twentieth magnitudes.

Entering into the structure of the stellar universe we have Single
Stars, Double Stars, Triple, Quadruple, and Multiple Stars, Temporary,
Periodical, and Variable Stars, Star-groups, Star-clusters, Galaxies,
and Nebulae.

SINGLE OR INSULATED STARS include all those orbs sufficiently isolated
in space so as not to be perceptibly influenced by the attraction of
other similar bodies. They are believed to constitute the centres of
planetary systems, and fulfil the purpose for which they were created by
dispensing light and heat to the worlds which circle around them.

The Sun is an example of this c