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SERIAL NO. 2631                                   PAGE 6.

Referring to Figure 2 again, it is to be noted that anywhere on the circle is equidistant from the sub-solar point. If one goes closer to the sub-solar point, the sun's altitude is greater; going one nautical mile towards to sub-solar point the altitude is increased by 1'; going inward 60 nautical miles the altitude is increased 1 [[degree symbol]]. If one goes outward from the circle, one nautical mile the altitude is decreased by 1'; 60 nautical miles it is decreased by 1[[degree symbol]], etc.
(A nautical or sea mile is 6080 feet ; a land or statute mile is 4280 ft.)
Astronomers know the position of the sun, moon and stars at any time throughout the year and this information is given in the Almanac.
The three points, viz., the (north) pole, the sub-solar point and the observer's position, may be considered to form a spherical triangle on the earth's surface with these points as vertices. If the observer's position and the sun's position are both known, it is possible to calculate by spherical trigonometry, not the sun's bearing and its altitude as measure from the observer's position. Observing from one fixed point,both the sun's altitude and bearing are changing constantly throughout the day.
To minimize calculations in the air the following methods are advocated.

[[underlined]]PRECOMPUTED TABLES, ETC.[[/underlined]]
Tables are prepared by a properly-trained person previous to flight and furnished to the observer before taking off. Each table is concerned with one point or station along the route. These stations should be near but not necessarily on the path to be flown over. The distance between these stations can not be greater than twice the width of the strip-maps. For convenience of the calculator, it is desirable that the station be located a whole number of degrees from the equator; this is not absolutely necessary, however.
The tables give the altitude and azimuth (hearing) of the sun asit would be measured by an observer located at the station. The altitufe and aximuths are given for every ten minutes of time.

Transcription Notes:
grammar and spelling errors kept as they are in the original document