DAVIS Mark 3 Sextant - Manual (Page 13)

THE ARTIFICIAL HORIZON
At times, it is not possible to see the natural horizon. Sun or moon shots may still
be taken, with the aid of an artificial horizon—a simple device containing water or
oil shielded from the wind (see below). It may be used by individuals exploring
inland far from the sea, or by students or experienced navigators to practice
celestial navigation without traveling to large bodies of water.
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Davis Instruments manufactures the Davis
#144 Artificial Horizon, pictured here. The
instrument is wind-proof and corrosion resis-
tant; its reflecting surface is completely
enclosed. Two sun shades and a lid are
included.
A generalized system of position determination which enables you to use obser-
vation of the sun and other celestial bodies made at times other than noon
requires knowledge of the navigation triangle, circles of equal altitude, assumed
position, and associated navigation tables such as the Nautical Almanac and
Sight Reduction Tables. These systems of celestial navigation are thoroughly stud-
ies and extensively used by serious navigators throughout the world.
Sets of work forms for the Sight Reduction Tables are used by nearly all naviga-
tors to help prevent errors and omissions in the calculation of celestial navigation
problems.
To use an artificial horizon:
1. Position the artificial horizon on level ground or other steady place. One end of
the artificial horizon should face directly into the sun so that a shadow is cast at
the opposite end. The sides and end facing the sun should be shadow-free.
2. Looking into the center of the liquid, move your head about so that you can see
the sun reflected on the liquid surface.
3. Bring the sextant to your eye and move the index arm of the sextant until you
see two suns—on reflected on the liquid and a double-reflected image on the
mirrors.