Campanola CAN18, Instruction Manual

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Brief explanation of astronomical terms
Celestial sphere This is an imaginary sphere used for displaying the visible positions
of celestial objects. The center is the observation point and the radius
is infinite. However, when as a figure, it is drawn as a finite one seen
from the outside.
Zenith This is the point where a line drawn vertically above (direction of
gravity) the point of observation intersects the celestial sphere. It
is the point on the celestial sphere that is directly above the point of
observation. This lunar age watch does not have the zenith (based on
35° N) as the display range of the celestial sphere (display range of the
azimuth/altitude lines).
Horizon This is the intersecting line between the celestial sphere and the plane
that is perpendicular to the vertical line (direction of gravity) that
includes the point of observation. The horizon (apparent altitude 0°,
true altitude approx. −0.57°) is not displayed on the transparent dial of
this lunar age watch. Instead, two lines are drawn: the thick one is the
sunrise/sunset line (true altitude approx. −0.84°) and the thin one near
above that is the moonrise/moonset line (true altitude approx. +0.38°).