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LESSON 20: Sight Reduction Using the Nautical Almanac and Pub 229

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

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LESSON 20: Sight Reduction Using the Nautical Almanac and Pub 229

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  1. LESSON 20:Sight Reduction Using the Nautical Almanac and Pub 229 • Learning 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. • 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.

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

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

  5. The Assumed Position • The 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 latitude that is an integer.

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

  7. Contents of the Nautical Almanac • Each 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)

  8. Contents of the Nautical Almanac • The 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

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

  10. Determining LHA and Declination of a Star • 4. GHA (star) = GHA (Aries) + SHA (star) • 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 LHA (star)= GHA (star) • + a λ (E) - a λ (W)

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

  12. Use of Pub 229 • 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.

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