LESSON 20:LESSON 20:Sight Reduction Using the Sight Reduction Using the

Nautical AlmanacNautical Almanac and Pub 229 and Pub 229

• Learning ObjectiveLearning Objective– Apply proper procedures to determine Apply proper procedures to determine

Hc and Zn for a celestial body using the Hc and Zn for a celestial body using the Nautical AlmanacNautical Almanac and Pub 229. and Pub 229.

Use of Pub 229Use of Pub 229

• DMA Publication 229 (the Marine DMA Publication 229 (the Marine Navigation Tables) is a set of tabulated Navigation Tables) is a set of tabulated solutions to the navigation triangle.solutions to the navigation triangle.

• If we know two of the sides and one of If we know two of the sides and one of the angles, we are able to extract the the angles, we are able to extract the remaining side and angle.remaining side and angle.

• This information, in conjunction with the This information, in conjunction with the altitude-intercept method, yields an LOP.altitude-intercept method, yields an LOP.

Use of Pub 229Use of Pub 229

• Entering arguments for Pub 229:Entering arguments for Pub 229:– Latitude (yields colatitude)Latitude (yields colatitude)– Declination (yields polar distance)Declination (yields polar distance)– LHA (yields meridian angle, t)LHA (yields meridian angle, t)

• These allow us to extractThese allow us to extract– Hc (coaltitude)Hc (coaltitude)– Z (quickly convertible to Zn)Z (quickly convertible to Zn)

Use of the Use of the Nautical AlmanacNautical Almanac

• The The Nautical AlmanacNautical Almanac is used to is used to determinedetermine– LHA (from GHA)LHA (from GHA)– declinationdeclination

For the celestial body used, at the time For the celestial body used, at the time of the observation.of the observation.

The Assumed PositionThe Assumed Position

• The assumed position is assumed The assumed position is assumed based uponbased upon– the ship’s DR position at the time of the the ship’s DR position at the time of the

celestial observation.celestial observation.– Ease of calculation:Ease of calculation:

• Use an assumed longitude (a Use an assumed longitude (a λλ) such that ) such that the LHA for entering Table 229 will be an the LHA for entering Table 229 will be an integer. integer.

• Use an assumed latitude that is an integer.Use an assumed latitude that is an integer.

Contents of the Contents of the Nautical Nautical AlmanacAlmanac

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

Contents of the Contents of the Nautical Nautical AlmanacAlmanac

• Each left hand page containsEach left hand page contains– GHA of Aries at hourly intervals GHA of Aries at hourly intervals – GHA and declination for the GHA and declination for the

navigational planets at hourly intervalsnavigational planets at hourly intervals– SHA and declination for all 57 SHA and declination for all 57

navigational stars (good for the entire 3 navigational stars (good for the entire 3 day period, since these values change day period, since these values change slowly)slowly)

Contents of the Contents of the Nautical Nautical AlmanacAlmanac

• The right hand page containsThe right hand page contains– GHA and declination at hourly intervals GHA and declination at hourly intervals

for the sun and the moonfor the sun and the moon– Rising and setting times for the sun and Rising and setting times for the sun and

the moonthe moon

Determining the LHA and Determining the LHA and the Declination of a Starthe Declination of a Star

1. Make the celestial observation, and 1. Make the celestial observation, and determine Ho from hs using the methods determine Ho from hs using the methods previously discussed.previously discussed.

2. Convert time of observation to GMT2. Convert time of observation to GMT

3. Enter the Nautical Almanac to find the 3. Enter the Nautical Almanac to find the GHA of Aries and the SHA of the starGHA of Aries and the SHA of the star

Determining LHA and Determining LHA and Declination of a StarDeclination of a Star

4. GHA (star) = GHA (Aries) + SHA (star)4. GHA (star) = GHA (Aries) + SHA (star) 5. Record Declination for the star 5. Record Declination for the star

(tabulated in the (tabulated in the Nautical AlmanacNautical Almanac)) 6. Calculate LHA of the star using the 6. Calculate LHA of the star using the

GHA of the star and assumed longitudeGHA of the star and assumed longitude LHA (star)= GHA (star)LHA (star)= GHA (star)

+ a + a λλ (E) (E) - a - a λλ (W) (W)

Use of Pub 229Use of Pub 229

• Now we knowNow we know– LHALHA– assumed latitudeassumed latitude– declinationdeclination

• We’re ready to enter Pub 229 and We’re ready to enter Pub 229 and find Hc and Z.find Hc and Z.

Use of Pub 229Use of Pub 229

• Now we enter Pub 229 and determine Now we enter Pub 229 and determine Hc and Z.Hc and Z.– Z is converted to ZnZ is converted to Zn– We now have Zn, Hc, and Ho. Now the We now have Zn, Hc, and Ho. Now the

celestial LOP can be plotted using the celestial LOP can be plotted using the altitude-intercept method.altitude-intercept method.