This interactive worksheet is designed to help learners understand how to calculate a simple Sun Line of Position (LOP) using American or British sight reduction tables.
The Celestial Course page includes eight fully worked exercises, allowing you to practise step by step and develop a thorough understanding of the method.
From personal experience, I have worked with marine officers who could perform sight reductions using tables significantly faster than I could with a calculator—proof that, in skilled hands, this traditional technique can still be remarkably effective.
This page presents only the solution to the La Rochelle exercise. I recommend mastering this exercise before moving on to the remaining seven.
The remaining exercises, along with their corrected answers, are available on the Celestial Course page.
The interactive worksheet provides immediate feedback on the accuracy of your answers, allowing you to assess your progress in real time and identify areas that need improvement.
The six sections
Ho = Observed altitude
LHA = Local Hour Angle
D = Declination of the Sun
Hc = Calculated altitude
Zv = True azimuth
Intercept = Difference between Ho and Hc
See the blank worksheet (PDF) for the tables.
Our observations on the La Rochelle exercise page
Now that you have determined the values shown in red using the observations from the La Rochelle exercise page, we can proceed with the calculations.
INTERACTIVE CELESTIAL WORKSHEET HO 229
Section 1
-Ho- (observed altitude)
We will calculate and explain Ho in two steps:
Step 1: Blue section
Apparent altitude and dip correction table for the Sun from EasySextant. Download
Apparent Altitude of the Sun (Ha) : Theory
Step 2: Red section
Apparent Altitude and dip correction table for the Sun from EasySextant. Download
Observed Altitude of the Sun (Ho) : Theory
Final result for this part of the worksheet: Hs → Ho.
INTERACTIVE CELESTIAL WORKSHEET HO 229
Section 2
Local Hour Angle (LHA)
GHA = _ _ ° _ _ ‘, _
+pp = _ _° _ _ ‘, _
GHA = _ _° _ _’, _
___________________
*G = _ _ ° _ _ ‘, _
_____________________
LHA = _ _ ° _ _ ‘, _
Add *G if east; subtract *G if west.
How to Calculate GHA + pp ( Increment)
Dead Reckoning Position: Latitude (L) and Longitude (G)
Section 3
-D- (Declination of the Sun)
D = _ _ ° _ _ ‘, _
correc. d = _ _ ° _ _ ‘, _
___________________
D = _ _ ° _ _ ‘, _
Section 4 and 5
Obtaining the Computed Altitude (Hc) and Azimuth (Zv) of the Sun Using Sight Reduction Tables
Before using the sight reduction tables, carefully review Section 6 below. ↓
Section 6
Intercept
Ho………….= _ _ ° _ _ ‘, _
Hc…………. = _ _ ° _ _ ‘, _
Intercept…= _ _ ° _ _ ‘, _
intercept = Ho – Hc
A positive intercept is plotted towards the Sun; a negative intercept is plotted away from the Sun.
Interactive Celestial Worksheet: Additional Knowledge
This section covers the time interval between two Lines of Position (LOPs), the procedure for transferring a LOP, and the uncertainty associated with a LOP.
Topics covered:
- The Sun’s LOP, running fixes, and uncertainty zones
- Planning the day using two Sun LOPs
- Determining latitude from a local apparent noon sight
- Calculating the time of local apparent noon
Using a Sun sight taken at local apparent noon is a widely adopted technique in maritime navigation.
It provides a straightforward and efficient method for determining latitude.
In summary
Remember that progress takes time and effort. If you feel overwhelmed or frustrated, take a short break from the worksheet before continuing.
A French-language version of this website is also available at www.ladroitedehauteur.com