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

• We know two of the sides and one of the We know two of the sides and one of the angles, and we are able to extract the angles, and 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

• The entering arguments for Pub 229 are:The entering arguments for Pub 229 are:– Latitude (colatitude)Latitude (colatitude)– Declination (polar distance)Declination (polar distance)– LHA (meridian angle)LHA (meridian angle)

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

• Let’s take another look at the navigation Let’s take another look at the navigation triangle...triangle...

Use of the Use of the Nautical AlmanacNautical Almanac

• The The Nautical AlmanacNautical Almanac is used to is used to determinedetermine– LHALHA– declinationdeclination

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

The Assumed PositionThe Assumed Position

• The assumed position is, of course, The assumed position is, of course, assumed, based uponassumed, based 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.

Contents of the Contents of the Nautical Nautical AlmanacAlmanac

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

• Let’s flip open to the daily pages and see Let’s flip open to the daily pages and see what information is available...what information is available...

Contents of the Contents of the Nautical Nautical AlmanacAlmanac

• The left hand page containsThe left hand page contains

• GHA at hourly intervals for AriesGHA at hourly intervals for Aries

• GHA and declination at hourly intervals for GHA and declination at hourly intervals for the navigational planetsthe navigational planets

• SHA and declination for all 57 navigational SHA and declination for all 57 navigational stars (good for the entire 3 day period, since stars (good for the entire 3 day period, since they only change very slowly)they only change very 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 moon and sunfor the moon and sun

• rising and setting information for the sun rising and setting information for the sun and moon (more on that later)and moon (more on that later)

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

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

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

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

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

4. GHA (star) = GHA (Aries) + SHA4. GHA (star) = GHA (Aries) + SHA

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 and assumed longitudeGHA and assumed longitude

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

Use of Pub 229Use of Pub 229

• Now we enter Pub 229 and determine Hc Now we enter Pub 229 and determine Hc and Z.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.

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