Line of Position — Peacock
See Rigil Kentaurus for a detailed explanation
of the steps here.
Computing a Line of Position takes these steps:
- Measure the object's altitude with a sextant, note exact time of
sight, correct sextant altitude for various errors.
- Use almanac to find GP of Peacock
- Pick an Assumed Position
- Use sight reduction tables to compute an azimuth (Z) to
the object and an expected altitude (Hc).
- Plot
Measure the object's altitude with a sextant
Leg 57 gives this information for the sighting
of Peacock:
- Time: 1999-03-24, 23:45:22
- Sextant Altitude: 22°24.8'
- Height of eye: 9 feet
- Index error: -2.5'
With this information, we can now fill in the first part of our
worksheet:
Object: Peacock
Hs: 22°24.8'
±ie -2.5
-dip -2.9
=Ha: 22°19.4
±corr: -2.3
=Ho: 22°17.1
Find Geographic Position of Peacock
date, time: 1999-03-24 23:45:22
almanac:
GHA: 166°58.3 v: _______ decl: S56°44.1 d: _______ HP: ______
+corr: 11°20.5 +d: ______
+v: ___._ =decl: ___°__._
+SHA: 53°36.9
=GHA: 231°55.7
±AP: ___°__._
=LHA: ___°__._
Pick an Assumed Position
Set AP to 54°S, 74°55.7W
date, time: 1999-03-24 23:45:22
almanac:
GHA: 166°58.3 v: _______ decl: S56°44.1 d: _______ HP: ______
+corr: 11°20.5 +d: ______
+v: ___._ =decl: ___°__._
+SHA: 53°36.9
=GHA: 231°55.7
±AP: -74°55.7
=LHA: 157°
Use Sight Reduction Tables
The table gives these values:
Again, Hc is within a degree of our Ho, which is a good sign.
Again, we go to the correction table and enter d (58) and the minutes
of declination (44). This gives 43
Sight reduction table:
Hc: 21°36 d: 58' Z: 194°
+d: 43
=Hc: 22°19
-Ho: 22°17
=dist: +2 +away, -towards
We are 2 nm further from Peacock than our assumed position.
Plot
Draw a vector from our assumed position in the direction 194°.
Measure 2 nm back along that vector and draw a line perpendicular
to the vector. This is our Line of Position for Peacock.
Our LOP's intersect almost at an exact spot. This
is a good sign. Now let's do the moon next.
Next: Line of Position — Moon