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The Celestial LOP
Determining the
Figure 9-8 illustrates the method used in establishing a single LOP by
LOP, continued
observing a star. An assumed position (AP) is selected according to
certain requirements of convenience in calculating (described later).
Observation of a star provides sextant altitude (hs). Sextant altitude is
then corrected to obtain observed altitude (Ho). The star’s altitude from
the assumed position, called the computed altitude (Hc), and its azimuth
angle are determined from tables by a procedure you will soon learn.
The azimuth angle is then converted to azimuth. After selecting an AP,
draw the azimuth through the AP. Along the azimuth, measure off the
altitude intercept (difference between the observed altitude and the
computed altitude). At the end of this measurement, draw a
perpendicular line, which is the LOP. You must know whether altitude
intercept (a) should be measured from AP toward the body or from AP
measured away from the body. It is helpful to remember the initials
Ho MO To, if Ho is more toward. This means that if Ho is greater than
Hc measure altitude intercept (a) from AP toward the body. If Hc is
greater than Ho measure altitude intercept (b) from AP away from the
body.
Figure 9-8. Determining a LOP.
9-17
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