Sight Reduction Using the Nautical Almanac and Pub 229

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)
• Lets take another look at the navigation
  triangle...

4
(No Transcript)
5
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.

6
The Assumed Position

• The assumed position is, of course, assumed,
  based upon
• the ships DR position at the time of the
  celestial observation.
• Ease of calculation.

7
Contents of the Nautical Almanac

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

8
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)

9
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)

10
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

11
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

12
Use of Pub 229

• Now we know
• LHA
• assumed latitude
• declination
• Were ready to enter Pub 229 and find Hc and Z.

13
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, well work through an example to
  illustrate the process...