The Heavens Above: A Popular Handbook of AstronomyRolfe, W. J. (William James)
Science
The Heavens Above: A Popular Handbook of Astronomy
Rolfe, W. J. (William James)
Astronomy
(2) The stars in the neighborhood of the depressed pole _never rise_.
The breadth of this belt also increases as the observer approaches the
pole, and decreases as he approaches the equator, to vanish entirely
when he reaches the equator. The distance from the depressed pole to the
margin of this belt is always equal to the latitude of the place.
(3) The stars in the neighborhood of the equinoctial, on the side of the
elevated pole, _set, but are above the horizon longer than they are
below it_. This belt of stars extends from the equinoctial to a point
whose distance from the elevated pole is equal to the latitude of the
place: in other words, the breadth of this third belt of stars is equal
to the complement of the latitude of the place. Hence this belt of stars
becomes broader and broader as the observer approaches the equator, and
narrower and narrower as he approaches the pole. However, as the
observer approaches the equator, the horizon comes nearer and nearer the
celestial axis, and the time a star is below the horizon becomes more
nearly equal to the time it is above it. As the observer approaches the
pole, the horizon moves farther and farther from the axis, and the time
any star of this belt is below the horizon becomes more and more unequal
to the time it is above it. The farther any star of this belt is from
the equinoctial, the longer the time it is above the horizon, and the
shorter the time it is below it.
(4) The stars which are in the neighborhood of the equinoctial, on the
side of the depressed pole, _rise, but are below the horizon longer than
they are above it_. The width of this belt is also equal to the
complement of the latitude of the place. The farther any star of this
belt is from the equinoctial, the longer time it is below the horizon,
and the shorter time it is above it; and, the farther the place from the
equator, the longer every star of this belt is below the horizon, and
the shorter the time it is above it.
At the equator every star is above the horizon just half of the time;
and any star on the equinoctial is above the horizon just half of the
time in every part of the earth, since the equinoctial and horizon,
being great circles, bisect each other.
8. _Vertical Circles._--Great circles perpendicular to the horizon are
called _vertical circles_. All vertical circles pass through the zenith
and nadir. A number of these circles are shown in Fig. 14, in which
_SENW_ represents the horizon, and _Z_ the zenith.
[Illustration: Fig. 14.]
The vertical circle which passes through the north and south points of
the horizon is called the _meridian_; and the one which passes through
the east and west points, the _prime vertical_. These two circles are
shown in Fig. 15; _SZN_ being the meridian, and _EZW_ the prime
vertical. These two circles are at right angles to each other, or 90°
apart; and consequently they divide the horizon into four quadrants.
[Illustration: Fig. 15.]
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