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well as the plotting of the fix are discussed later.
9.6. Postcomputation Method. The steps in this procedure are as follows:
9.6.1. Determine the GHA of Aries for the time of observation from the Air Almanac.
9.6.2. Assume a position as close as possible to the DR position at the time of the shot so the latitude and
LHA of Aries in whole degrees may be determined.
9.6.3. Turn to the page in Pub. No. 249 for the assumed latitude and, opposite the LHA of Aries, select
the stars to be shot. In making the selection, assume the LHA of Aries will change 1o every 4 minutes of
time.
9.6.4. Shoot the body and record the time, Ho, and name of the body.
9.6.5. Obtain the GHA of Aries for the time of the observation, and apply the assumed longitude to
determine the LHA of Aries.
9.6.6. Turn to the pages for the assumed latitude and, opposite the LHA of Aries in the column headed
by the name of the star, find and record the Hc and Zn.
9.7. Pub. No. 249, Volumes 2 and 3. Volume 1 consists of tables of Hc and Zn for selected stars.
Because the Dec and SHA of each star change slowly, these tables may be used for many years with
only small corrections. The Dec and SHA of a nonstellar body change rapidly, making a permanent
format similar to Volume 1 impossible for the sun, moon, and planets.
9.7.1. Volumes 2 and 3 have Dec tables adequate for determining the Hc and Zn of any celestial body
within the Dec range of 30o N to 30o S. They are intended primarily for use when observing nonstellar
(solar system) bodies. Volume 2 provides latitudes between 39o N and 39o S, and Volume 3 provides for
latitudes from 40o N or S to the poles.
9.7.2. Provision is made for observed altitudes from 90o above to 3o below the horizon (7o from latitudes
70o to the pole). In view of refraction and of possible long intercepts, the tables are actually extended 2o
below these limits.
GHA Aries for 0230 GMT 196o06'
Correction for 4 minutes 1o00'
GHA Aries for 0234Z 197o06'
Closest longitude for whole LHA W075o06' (assumed longitude)
LHA Aries for 0234Z 122o
222 AFPAM11-216 1 MARCH 2001
9.8. Entering Arguments. Volumes 2 and 3 are entered with the LHA of the body, in contrast to
Volume 1, which is entered with the LHA of Aries. The range extends from 0o through all LHAs
applicable within the altitude limits of the body. Between latitude 70o and the pole, the LHA interval is
2o; for latitudes below 70o, the interval is 1o. Arguments of LHA of the body less than 180o appear on
the left margin, and arguments greater than 180o appear on the right.
9.8.1. Several pages are devoted to each degree of latitude. Each page has 15 declination columns and is
labeled with its value at the top and bottom. Each page is also marked Declination Contrary Name to
Latitude or Declination Same Name as Latitude.
9.8.2. The entering arguments of LHA of the body, for declination of contrary name to latitude, always
increase from the bottom of the page on the left side, and decrease on the right. The opposite
arrangement exists on pages where Dec and latitude has the same name. Occasionally, one page will be
blank in the middle and the top half will cover Declination Same Name as Latitude, while the bottom
half will be Declination Contrary Name to Latitude.
9.8.3. Azimuth angle (Z) is listed instead of true azimuth (Zn). Since Zn is used for plotting, it is
necessary to convert Z to Zn. The rules for conversion are listed on the left-hand side at the top and
bottom of every page. Notice that LHA and Zn will never occur on the same side of 180o.
9.8.4. In addition to Hc and Z, a value of d is also listed. This d-value is the change in altitude (Hc) with
a 1o increase in Dec. If the LHA and Dec of the body and the latitude of the assumed position are each a
whole number of degrees, the Hc and Z are found in the correct Dec column opposite the LHA of the
body on the page marked by the proper latitude value.
9.8.5. For example, refer to the portion of the table shown in Figure 9.6. At the latitude 40o N, if the
LHA of a body is 86o and its Dec is 5o N, the Hc is 06o16' and the azimuth angle (Z) is 089o. The rule in
the upper left-hand corner of the page applies for the conversion of Z to Zn. Zn = (360o – Z) or (360o –
089o) = 271o. Here again the position is assumed so that latitude and LHA are whole numbers.
9.9. Interpolation for Declination (Dec). When the Dec of a body is a number of minutes in addition to
a whole number of degrees, the altitude (Hc) is extracted for the whole number of degrees and corrected
by interpolation for the additional minutes. There is rarely a need for interpolation of Z, which is given
only to the nearest degree.
9.9.1. Interpolation for Hc should always be made in the direction of increasing Dec in accordance with
　
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