1. LESSON 20: Sight Reduction Using the Nautical Almanac and Pub 229 Learning ObjectiveLearning Objective –Apply proper procedures to determine Hc and Zn for a celestial body using the Nautical Almanac and Pub 229.

2. Use of Pub 229 DMA Publication 229 (the Marine Navigation Tables) is a set of tabulated solutions to the navigation triangle.DMA Publication 229 (the Marine Navigation Tables) is a set of tabulated solutions to the navigation triangle. If we know two of the sides and one of the angles, we are able to extract the remaining side and angle.If we know two of the sides and one of the angles, we are able to extract the remaining side and angle. This information, in conjunction with the altitude-intercept method, yields an LOP.This information, in conjunction with the altitude-intercept method, yields an LOP.

3. Use of Pub 229 Entering arguments for Pub 229:Entering arguments for Pub 229: –Latitude (yields colatitude) –Declination (yields polar distance) –LHA (yields meridian angle, t) These allow us to extractThese allow us to extract –Hc (coaltitude) –Z (quickly convertible to Zn)

5. Use of the Nautical Almanac The Nautical Almanac is used to determineThe Nautical Almanac is used to determine –LHA (from GHA) –declination For the celestial body used, at the time of the observation. For the celestial body used, at the time of the observation.

6. The Assumed Position The assumed position is assumed based uponThe assumed position is assumed based upon –the ship’s DR position at the time of the celestial observation. –Ease of calculation: Use an assumed longitude (a λ) such that the LHA for entering Table 229 will be an integer.Use an assumed longitude (a λ) such that the LHA for entering Table 229 will be an integer. Use an assumed latitude that is an integer.Use an assumed latitude that is an integer.

7. Contents of the Nautical Almanac The daily pages of the Nautical Almanac contain a variety of information, presented three days at a time.The daily pages of the Nautical Almanac contain a variety of information, presented three days at a time.

8. Contents of the Nautical Almanac Each left hand page containsEach left hand page contains –GHA of Aries at hourly intervals –GHA and declination for the navigational planets at hourly intervals –SHA and declination for all 57 navigational stars (good for the entire 3 day period, since these values change slowly)

9. Contents of the Nautical Almanac The right hand page containsThe right hand page contains –GHA and declination at hourly intervals for the sun and the moon –Rising and setting times for the sun and the moon

11. Determining the LHA and the Declination of a Star 1. Make the celestial observation, and determine Ho from hs using the methods previously discussed. 1. Make the celestial observation, and determine Ho from hs using the methods previously discussed. 2. Convert time of observation to GMT 2. Convert time of observation to GMT 3. Enter the Nautical Almanac to find the GHA of Aries and the SHA of the star 3. Enter the Nautical Almanac to find the GHA of Aries and the SHA of the star

12. Determining LHA and Declination of a Star 4. GHA (star) = GHA (Aries) + SHA (star) 4. GHA (star) = GHA (Aries) + SHA (star) 5. Record Declination for the star (tabulated in the Nautical Almanac) 5. Record Declination for the star (tabulated in the Nautical Almanac) 6. Calculate LHA of the star using the GHA of the star and assumed longitude 6. Calculate LHA of the star using the GHA of the star and assumed longitude LHA (star)= GHA (star) LHA (star)= GHA (star) + a λ (E) - a λ (W) + a λ (E) - a λ (W)

13. Use of Pub 229 Now we knowNow we know –LHA –assumed latitude –declination We’re ready to enter Pub 229 and find Hc and Z.We’re ready to enter Pub 229 and find Hc and Z.

14. Use of Pub 229 Now we enter Pub 229 and determine Hc and Z.Now we enter Pub 229 and determine Hc and Z. –Z is converted to Zn –We now have Zn, Hc, and Ho. Now the celestial LOP can be plotted using the altitude-intercept method.