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body or other automatic systems such as INS or GPS.
272 AFPAM11-216 1 MARCH 2001
12.16.1. At high latitudes, the sun's daily motion is nearly parallel to the horizon. The motion of the
aircraft in these regions can easily have greater effect upon altitude and Zn of the sun than the motion of
the sun itself.
12.16.2. At latitude 64o, an aircraft flying west at 400k keeps pace with the sun, which appears to remain
stationary in the sky. At higher latitudes, the altitude of a celestial body might be increasing at any time
of day, if the aircraft is flying toward it and a body might rise or set, at any azimuth, depending upon the
direction of motion of the aircraft relative to the body.
12.17. Bodies Available for Observation. During the continuous daylight of the polar summer, only the
sun is regularly available for observation. The moon is above the horizon about half the time, but
generally it is both visible and at a favorable position with respect to the sun for only a few days each
month.
12.17.1. During the long polar twilight, no celestial bodies may be available for observation. As in lower
latitudes, the first celestial bodies to appear after sunset and the last to remain visible before sunrise are
those brighter planets, which are above the horizon.
12.17.2. The sun, moon, and planets are never high in polar skies, thus making low altitude observations
routine. Particularly with the sun, observations are made when any part of the celestial body is visible. If
it is partly below the horizon, the upper limb is observed and a correction of -16' for semidiameter (SD)
is used in the SD block of the precomputation form.
12.17.3. During the polar night, stars are available. Polaris is not generally used because it is too near the
zenith in the arctic and not visible in the Antarctic. A number of good stars are in favorable positions for
observation. Because of large refractions near the horizon avoid low altitudes (below about 20o) when
higher bodies are visible.
12.18. Sight Reduction. Sight reduction in polar regions presents some slightly different problems from
those at lower latitudes. Remember, for latitudes greater than 69o N or 69o S, Pub. No. 249 tables have
tabulated Hcs and azimuths for only even degrees of LHA. This concerns you in two ways. First, it will
be necessary to adjust assumed longitude to achieve a whole, even LHA for extractions. This will
preclude interpolating. Second, the difference between successive, tabulated Hcs is for 2o of LHA, or 8
minutes of time, so this difference must be divided in half when computing motion of the body for 4
minutes of time.
12.18.1. For ease of plotting, all azimuths can be converted to grid. To convert, use the longitude of the
assumed position to determine convergence because the Zn is for the assumed position, not the DR
position. On polar charts, convergence is equal to longitude.
12.18.2. In computing motion of the observer, it is imperative that you use the difference between grid
azimuth and grid track, or Zn and true track, since this computation is based on relative bearing (RB).
Zn minus grid course does not give relative bearing.
12.18.3. Since low altitudes and low temperatures are normal in polar regions, refer to the refraction
correction table and use the temperature correction factor for all observations.
12.18.4. In polar regions, Coriolis corrections reach maximum values and should be carefully computed.
AFPAM11-216 1 MARCH 2001 273
12.19. Poles as Assumed Positions. Within approximately 2o of the pole, it is possible to use the pole as
the assumed position. With this method, no tabulated celestial computation is necessary and the position
may be determined by use of the Air Almanac alone.
12.19.1. At either of the poles of the earth, the zenith and the elevated poles are coincident or the plane
of the horizon is coincident with the plane of the equator. Vertical circles coincide with the meridians
and parallels of latitude coincide with Dec circles. Therefore, the altitude of the body is equal to its Dec
and the azimuth is equal to its hour angle.
12.19.2. To plot any LOP, an intercept and the azimuth of the body are needed. In this solution, the
elevated pole is the assumed position. The azimuth is plotted as the GHA of the body, or the longitude
of the subpoint. The intercept is found by comparing the Dec of the body, as taken from the Air
Almanac, with the observed altitude of the body. To summarize, the pole is the assumed position, the
Dec is the Hc, and the GHA equals the azimuth.
12.19.3. For ease of plotting, convert the GHA of the body to grid azimuth by adding or subtracting 180o
when using the North Pole as the assumed position. When at the South Pole, 360o – GHA of the body
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