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Sight Reduction Using the Nautical Almanac and Pub 229

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. DMA Publication 229 is nothing more than tabulated solutions to the navigation triangle.

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Sight Reduction Using the Nautical Almanac and Pub 229

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  1. 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 is nothing more than tabulated solutions to the navigation triangle. • We know two of the sides and one of the angles, and 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 • The entering arguments for Pub 229 are: • Latitude (colatitude) • Declination (polar distance) • LHA (meridian angle) • These allow us to extract • Hc (coaltitude) • Zn (Z) • Let’s take another look at the navigation triangle...

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

  5. The Assumed Position • The assumed position is, of course, assumed, based upon • the ship’s DR position at the time of the celestial observation. • Ease of calculation.

  6. Contents of the Nautical Almanac • The daily pages of the Nautical Almanac contain a variety of information, presented three days at a time. • Let’s flip open to the daily pages and see what information is available...

  7. Contents of the Nautical Almanac • The left hand page contains • GHA at hourly intervals for Aries • GHA and declination at hourly intervals for the navigational planets • SHA and declination for all 57 navigational stars (good for the entire 3 day period, since they only change very slowly)

  8. Contents of the Nautical Almanac • The right hand page contains • GHA and declination at hourly intervals for the moon and sun • rising and setting information for the sun and moon (more on that later)

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

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

  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. • At this point, we’ll work through an example to illustrate the process...

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