Table of Contents

Class Prep

Class 1
Class 2
Class 3
Class 4
Class 5
Class 6
Class 7
Class 8
Class 9
Class 10

>>Topical Articles<<
Assumed Longitude
Casio fx-260 Solar II
Emergency Navigation
Making a Kamal
Noon Sight
Pub. 249 Vol. 1
Sextant Adjustment
Sextant Skills
Sight Averaging
Sight Planning,
  Error Ellipses,
  & Cocked Hats
Slide Rules
Standard Terminology
Star Chart
The Raft Book
Worksheet Logic

Assumed Longitude and the Meridian Angle

Let me take another stab at assumed longitudes and meridian angles for when you are in the eastern hemisphere. If you are in the eastern hemisphere, and the GP is also in the eastern hemisphere then you could:

  1. Convert the GHA into an East-Longitude value by subtracting the GHA from 360° 00.0'.
  2. For your aλ, take the whole-degree from your DR position.
  3. For the minutes in your aλ, use the minutes from the East-Longitude version of the GHA.
  4. Subtract the smaller value from the larger value.

If you are in the eastern hemisphere and the GP is in the western hemisphere, then:

  1. For your whole-degree of your aλ, use your DR whole-degree.
  2. For the minutes in your aλ, take the minutes from the GHA and subtract them from 60.0'.
  3. Add the GHA to your aλ for the meridian angle.

In either case, once you have your aλ, if it is more than 30' away from your DR, you may adjust the whole-degree portion of your aλ (and consequently, the meridian angle) to get the aλ closer to the DR. This should keep your intercepts shorter, and may contribute to a slightly more accurate fix.

For instance, if you are in Caesarea and your DR λ is E 34° 53.5' and your aλ is initially 34° 02.8', with a meridian angle of W 22°, you might elect to modify your aλ and make it 35° 02.8', giving you a meridian angle of W 23°.

The above is the best I can do...but you may find our textbook more helpful. It addresses this in the lower left corner of page 152.

Since that is a pretty brief treatment, I am including some pages from a textbook I used back in the early 1980s.