Astronomy in a nutshell : $b The chief facts and principles explained in popular language for the general reader and for schoolsServiss, Garrett Putman
Science
Astronomy in a nutshell : $b The chief facts and principles explained in popular language for the general reader and for schools
Serviss, Garrett Putman
Astronomy -- Juvenile literature
Note the clustering of stars over the whole field, the intricate forms
of the nebula, and particularly the curious black spots, or “holes,”
resembling drops of ink.
]
The Harvest Moon and the Hunter's Moon, which are popularly celebrated
not only on account of their romantic associations, but also because in
some parts of the world they afford a useful prolongation of light after
sunset, occur only near the time of the autumnal equinox, and they are
always full moons. The full moon nearest the date of the equinox,
September 23d, is the Harvest Moon, and the full moon next following is
the Hunter's Moon. Their peculiarity is that they rise, for several
successive evenings, almost at the same hour, immediately after sunset.
This is due to the fact that at that time of the year the ecliptic, from
which the moon's path does not very widely depart, is, in high
latitudes, nearly parallel with the horizon.
The full moon in winter runs higher in the sky, and consequently gives a
brighter light, than in summer. The reason is because, since the full
moon must always be opposite to the sun, and since toe sun in winter
runs low, being south of the equator, the full moon rides proportionally
high.
=5. Eclipses.= We have mentioned the connection of the moon with the
tides, but there is another phenomenon in which the moon plays the most
conspicuous part—that of eclipses. There are two kinds of eclipses—solar
and lunar. In the former it is the moon that causes the eclipse, by
hiding the sun from view; and in the latter it is the moon that suffers
the eclipse, by passing through the shadow which the earth casts into
space on the side away from the sun. In both cases, in order that there
may be an eclipse it is necessary that the three bodies, the moon, the
sun, and the earth, shall be nearly on a straight line, drawn through
their centres. Since the moon occupies about a month in going round the
earth there would be two eclipses in every such period (one of the sun
and the other of the moon), if the moon's orbit lay exactly in the plane
of the ecliptic, or of the earth's orbit. But, in fact, the orbit of the
moon is inclined to that plane at an angle of something over 5°. Even
so, there would be eclipses every month if the two opposite points,
called nodes, where the moon crosses the plane of the ecliptic, always
lay in a direct line with the earth and the sun; but they do not lie
thus. If, then, the moon comes between the earth and the sun when she is
in a part of her orbit several degrees above or below the plane of the
ecliptic, it is evident that she will pass either above or below the
straight line joining the centres of the earth and the sun, and
consequently cannot hide the latter. But, since eclipses do occur in
some months and do not occur in others, we must conclude that the
situation of the nodes changes, and such is the fact. In consequence of
the conflicting attractions of the sun and the earth, the orbit of the
Public-domain text, read in full here on John Shaqi.
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