Transcript 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
• 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.
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)
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.
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.
Contents of the Nautical
Almanac
• The daily pages of the Nautical
Almanac contain a variety of
information, presented three days at
a time.
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)
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
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
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
+ a λ (E)
LHA (star)= GHA (star) - a λ (W)
Use of Pub 229
• Now we know
– LHA
– assumed latitude
– declination
• We’re ready to enter Pub 229 and
find Hc and Z.
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.