An introduction to astronomy: designed as a text-book for the use of students in college. By Denison Olmsted ...

18 THE EARZTH.
pole must be in his horizon. The celestial equator coincides
with his prime vertical, being a great circle passing through
the east and west points. Since all the diurnal circles are parallel to the equator, they are all, like the equator, perpendicullar to his horizon. Such a view of the heavenly bodies is
called a right sphere; or,
A RIGHT SPHERE IS one if Which all thle daily revolttions of
the heavenly bodies are in circles perpendictclar to the horizon.
A right sphere is seen only at the equator. Any star situated in the celestial equator, would appear to rise directly in
the east, to pass the meridian in the zenith of the spectator,
and to set directly in the west. In proportion as stars are at a
greater distance from the equator towards the pole, they describe smaller and smaller circles, until, near the pole, their
motion is hardly perceptible. In a right sphere every star remains an equal time above and below the horizon; and since
the times of their revolutions are equal, the velocities are as
the lengths of the circles they describe. Consequently, as the
stars are more remote from the equator towards the pole, their
motions become slower, until, at the pole, if a star were there,
it would appear stationary.
50. If the spectator advances one degree towards the north
pole, his horizon reaches one degree beyond the pole of the
earth, and cuts the starry sphere one degree below the pole of
the heavens, or below the north star if that be taken as the
place of the pole. As he moves onward towards the pole, his
horizon continually reaches further and further beyond it, until,
when he comes to the pole of the earth, and under the pole of
the heavens, his horizon reaches on all sides to the equator, and
coincides with it. Moreover, since all the circles of daily motion are parallel to the equator, they become, to the spectator
at the pole, parallel to the horizon. This is what constitutes a
parallel sphere. Or,
A PARALLEL SPHERE is that in which all the circles of dtily
zotion are parallel to the horizon.
51. To render this view of the heavens familiar, the learner
should follow round in his mind a number of separate stars,
one near the horizon, one a few degrees above it, and a third