Table of Contents |
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: - Convert the GHA into an East-Longitude value by subtracting the GHA from 360° 00.0'.
- For your aλ, take the whole-degree from your DR position.
- For the minutes in your aλ, use the minutes from the East-Longitude version of the GHA.
- Subtract the smaller value from the larger value.
If you are in the eastern hemisphere and the GP is in the western hemisphere, then: - For your whole-degree of your aλ, use your DR whole-degree.
- For the minutes in your aλ, take the minutes from the GHA and subtract them from 60.0'.
- 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
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 3 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. |