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anticipates being at 18o N 135o W at 0015Z on 28 September 1995. There are several bodies listed in the
Air Almanac, but not all of them are available for observation. To determine availability, take the
observer's longitude and look 80o either side of it. Within this range, compare the GHA of a body.
Looking at Figure 12.1 we see that the sun, moon, Venus, and Jupiter are within the 80o range and are
therefore usable. Saturn is outside of the 80o range so it is not usable. The declination of a body is not
normally a factor; however, at high latitudes a body may not be available when its subpoint is near the
pole opposite the observer.
Figure 12.1. A Quick Check of Body Availability.
12.3. Latitude by Polaris. Polaris is the polestar, or North Star. Because Polaris is approximately 1o
from the North Pole, it makes a small diurnal circle and seemingly stays in about the same place all
night. This fact makes Polaris very useful in navigation. With certain corrections, it serves as a reference
point for direction and for latitude in the Northern Hemisphere. Latitude by Polaris is a quick method of
obtaining a latitude line of position (LOP); only the tables given in the Air Almanac are needed.
AFPAM11-216 1 MARCH 2001 255
12.3.1. Obtaining Latitude by Polaris. A latitude by Polaris LOP is obtained by applying the "Q"
correction (Figure 12.2) to the corrected observed altitude. This adjusts the altitude of the pole, which is
equal to the navigator's latitude. The Q correction table is in the back of the Air Almanac. The entering
argument for the table is exact local hour angle (LHA) of Aries. The effect of refraction is not included
in Q correction, so the observed altitude must be fully corrected. When refraction is used for a latitude
by Polaris LOP, it is applied to the observed altitude and the sign of the correction is negative. A Polaris
LOP can also be plotted using the intercept method. In this case, the Hc is computed by reversing the
sign of the Q correction and applying it to the assumed latitude (rounded off to the nearest degree).
Refraction is positive when applied to get an Hc for the intercept method.
12.3.2. Obtaining Azimuth of Polaris. For either method, the azimuth of Polaris is obtained from the
Azimuth of Polaris table found in the Air Almanac or in the Pub. No. 249 (Figure 12.2). Whether plotted
as an intercept or a latitude, the assumed position should be corrected for Coriolis or rhumb line and
precession or nutation. The resulting LOPs should fall in the same place for either method. To plot the
LOP using the latitude method, choose the longitude line closest to the DR and plot perpendicular to the
longitude line. For the intercept method, use the assumed latitude and plot the intercept normally using
the azimuth of Polaris.
256 AFPAM11-216 1 MARCH 2001
Figure 12.2. Polaris Q Correction and Azimuth Tables From the Air Almanac.
AFPAM11-216 1 MARCH 2001 257
Figure 12.3. Plotting the Polaris LOP.
12.3.3. Latitude by Polaris Example. On 18 April 1995 for Greenwich mean time (GMT) 1600 at 23o-
10' N 120o W, with an observed altitude 23o-06' at 31,000'. When doing a latitude by Polaris you must
use the exact latitude and longitude. See Figure 12.3 for plotting.
GHA 086o-18'
Longitude (West) -120o-00'
LHA 326o-18'
True Course (TC) = 090o
Groundspeed (GS) = 400 knots
Coriolis/rhumb line = 7R
Corrected Observed Altitude 23o-06'
Q (based on LHA 072-44) -15'
Refraction -01'
Latitude 22o-50'
Azimuth (LHA 326o-18', Latitude 23oN) = 000.8o
NOTE: If the Q correction table in Volume 1 is used, precession and nutation (P/N) and Coriolis or
rhumb line must be used in plotting the LOP. This is because the Pub. No. 249 covers a 5-year period
and the further the years get from the Epoch year, the greater the error is when using the Polaris table.
P/N compensates for this error.
258 AFPAM11-216 1 MARCH 2001
12.3.4. Intercept Method Example. Referring to the previous problem (see Figure 12.3 for plotting).
NOTE: Applying 10A to assumed latitude gives 22o-50' N, which is the same the answer in the latitude
by Polaris example.
Azimuth of Polaris = 359.5
Coriolis/rhumb line = 7R
Assumed Lat (rounded off) 23o-00'N
Q (Reversed Sign) +15'
Refraction +01'
Hc Polaris 23o-16'
Ho Polaris 23o-06'
Intercept 10A
NOTE: In these examples all information was taken from the Air Almanac. No P/N is required.
Section 12B— LHA Method of Fixing
12.4. LHA Method of Obtaining Three-Star Fix. The LHA technique allows you to solve the motion
problem for a three-star fix by applying a correction to the assumed position rather than computing a
numerical solution on the precomp. This eliminates mathematical motion calculations, therefore
　
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