How to calculate a celestial Line Of Position

This is just a response page on how to calculate a celestial Line Of Position, resulting from the ‘La Rochelle exercise,‘ a primary exercise designed to lead you through all the classical steps for both calculating and understanding the theoretical part. 

Ultimately, it enables you to plot the Line of Position (LOP) on a nautical chart or plotting sheet and find your way at sea

How to calculate a celestial Line Of Position, voyage planning ocean passages for the world
Classic volume on ocean voyage planning

You will be redirected to this page in the La Rochelle exercise.

1)Answer for La Rochelle exercise: scientific calculator

2)Answer for La Rochelle exercise: logarithm and azimuth tables


1)Answer for La Rochelle exercise: scientific calculator

How to calculate a celestial Line Of Position, scientific calculator with dms function

Lighthouse and Rough Sea. Author image: photo fiddler from Canada

For our purpose, we only need a few functions of the scientific calculator, and they are all explained in the interactive worksheet.


Free exercise easysextant solution,image of birds
Birds at the beach. Author image: Wikipedia account100

How to calculate a celestial Line Of Position:

2)Answer for La Rochelle exercise: logarithm and azimuth tables

Free exercise easysextant: solution logarithm table
How to calculate a celestial Line Of Position,  5 tables  logarithms open for calculation of the La Rochelle exercise

The use of the tables

However, this course which is based on the alternative approach based on logarithm tables is less enriching for students in merchant marine schools.

In France, around 1980, they formalized the use of calculators.

Indeed, sailors who navigate ocean passages around the world are the main target audience for this course.

A compass. Aalborg Denmark. Author image: Thomasz Sienicki

Certainly, also intended for both professional mariners who operate trans ocean conveying vessels and mariners who participate in offshore races without electronic instruments.

In fact with some practice, one can become faster with tables than with a calculator.

During my time as a trainee, I completed more than 300 sight calculations with the officers on board.

I always used my calculator, while they always used logarithm tables. However, I never beat them in terms of speed.


Seagull at the ocean. Author image: Bplay40

How to calculate a celestial Line Of Position:

La Rochelle is situated where?

Indeed, La Rochelle situates on the southwestern coast of France.

It is a port city located in the Charente-Maritime department, in the region of Nouvelle-Aquitaine.

La Rochelle, located on the Bay of Biscay, renowned for its picturesque harbor, historic architecture, and maritime heritage.

Also, beautiful beaches and islands surround the city, making it a popular tourist destination.

Additionally, La Rochelle has a rich cultural scene, with museums, theaters, and festivals attracting visitors year-round.