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the terrestrial triangle is also called Co-Lat on the celestial triangle. To be perfectly correct, the term on
the celestial sphere corresponding to latitude on the earth is declination (Dec); therefore, the celestial
side could well be called co-declination of the zenith of the assumed position.
AFPAM11-216 1 MARCH 2001 219
Figure 9.4. Co-Altitude Equals 90 Minus Hc.
9.4.3. Rather than have this confusion, the terrestrial term Co-Lat is also used with reference to the
celestial sphere, just as latitude of the subpoint is considered to be the Dec amount from the equator.
Latitude is used when referring to the observer or zenith, and Dec is used when referring to the star or its
subpoint. The distance between the subpoint and the assumed position is generally referred to as zenith
distance (Co-Alt) rather than the segment of the vertical circle joining the subpoint and the assumed
position. These angular distance terms are interchangeable on the celestial and terrestrial spheres.
9.4.4. The values of the Zn and the interior angle (Z) are listed in the Pub. No. 249 tables depending
upon whether or not a Dec solution is desired. Pub. No. 249, Volume 1, lists the Zn rather than the
interior angle. Pub. No. 249, Volumes 2 and 3, list the interior angle (Z). It is necessary to follow rules
printed on each page to convert the interior angle (Z) to true azimuth (Zn).
9.5. Pub. No. 249, Volume 1. This volume deals solely with the solution concerning selected stars and
is considered separately from Volumes 2 and 3. Volume 1 provides complete worldwide coverage from
pole to pole for each degree of latitude. The LHA of Aries is listed in 1o increments from latitudes of 0o
to 69o North and South inclusive. From 70o through 89o of latitude, the meridians are so close together
that it is only necessary to tabulate the values of the LHA of Aries in even 2o increments. There are two
pages devoted to each whole degree of latitude between latitudes 69o N and 69o S inclusive. From there
to the pole, only one page is devoted to each whole degree of latitude. The three stars marked by
diamonds on each page provide sets for fixing purposes, which are favorably situated in altitude and
azimuth.
9.5.1. The entering arguments are the assumed latitude and the LHA of Aries (to whole degrees). At any
one time, the navigator has the choice of the seven listed stars for that latitude plus Polaris. The names
of the stars are in capital letters if the star is of first magnitude or brighter; the second magnitude stars
are printed in small letters. The names of the stars are listed every 15o of LHA of Aries (every 30o in the
polar latitudes). For the time the navigator expects to make an observation, commonly called a shot, they
look up the GHA of Aries and apply the approximate longitude to get a whole degree LHA of Aries. The
220 AFPAM11-216 1 MARCH 2001
navigator then enters Pub. No. 249, Volume 1, with the latitude closest to the dead reckoning (DR)
latitude and the LHA of Aries to select the stars that will be shot.
9.5.2. Since single celestial observation results in only one LOP, it is necessary to shoot two or more
bodies to obtain a fix. Suppose the navigator wants to shoot at approximately 0230 Greenwich Mean
Time (GMT), he or she looks up the GHA of Aries (in the Air Almanac) and finds it to be 196o. The DR
position for this time is 31o48' N, 075o26' W. A quick calculation shows the LHA of Aries is
approximately 121o, and the closest latitude is 32o N. Notice in the portion of the tables reproduced in
Figure 9.5 the available stars at this position are Alkaid, Regulus, Alphard, Sirius, Rigel, Aldebaran, and
Capella. Using Sirius, a shot is taken at 0231 and the Ho obtained is 37o50'.
GHA Aries for 0230 GMT 196o06'
Correction for l minute 15'
GHA Aries for 0231 GMT 196o21'
Closest longitude to DR for whole LHA W075o21' (assumed longitude)
LHA Aries for 0231 GMT 121o
Figure 9.5. Enter Tables With LHA Aries and Latitude.
9.5.3. The closest whole degree of latitude is 32o N; therefore, it is used as the assumed latitude. The
assumed longitude is selected as the closest point, resulting in an LHA of Aries that is a whole degree
(no minutes). The Hc of Sirius is listed as 37o40'. The Zn is 205o.
AFPAM11-216 1 MARCH 2001 221
9.5.4. The second shot was taken at 0234 using Regulus, the Ho being 55o30'. A new DR position could
be obtained for 0234 GMT, but the 0230Z DR position will suffice for this determination of Hc and Zn.
9.5.5. The assumed latitude is still 32o N and, in this case, 075o06' W is the assumed longitude since this
is the closest longitude to the DR longitude that results in the LHA of Aries being a whole degree. The
Hc of Regulus is listed as 56o19', and the Zn is 119o. The various corrections that must be applied as
　
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