This page explains ancestral celestial Douwes formula, a logarithm-based method featured in the second part of my worksheet

View first Astronavigation and Logarithm Option from easysextant.com

In fact, this formula allows you to calculate the sun’s height using only logarithm tables, without the necessity of a scientific calculator.

Table 1 = log cos; Table 2 = log versine; Table 3 cosine

The main objective of this website is to assist in determining your sea position with a sextant, with a primary focus on utilizing a scientific calculator, although the option to employ logarithm tables is also available.

However, understanding the Douwes formula is not a prerequisite for utilizing the tables.

**Hence, you may skip this page without encountering any issues in utilizing the tables**

Also, after starting the La Rochelle exercise, you will have the option of using a calculator or logarithm tables.

### ancestral celestial Douwes formula: explanation Douwes formula

Also, to work with this formula without a calculator we will use the logarithm tables and the natural sine and cosine tables

### First part of the formula

L = Dead reckoning latitude

D = Declination of the sun

SAME NAME/NOT SAME NAME is part of the logarithm method.In this part we **do not use** the rule of signs .

### Ancestral celestial Douwes formula: second part of the Douwes formula

logarithm 2nd term

## Table 1 et 2

Ancestral celestial Douwes formula:

## Table 3, 4 et 5

Finally, after having found **log 2nd Term**, we will seek with the help of table 4 (logarithms of whole numbers) **the natural 2nd Term**

Consequently, with the result ** natural cos (L+/-D) ⎼ natural 2eT = sin Hc**, we will find the sin Hc.

example: sin Hc = 0,5

Hc = arcsin (0,5) = 30° (Table 5)

Additionally, here you can find a total of 4 exercises, all fully worked out and provided with the necessary table pages.

Two exercises Hc with logarithm tables and solutions

La Rochelle exercise option logarithm tables

Furthermore, after completing those four exercises, you can consider buying the solutions to the seven remaining exercises in the store, which will come with the complete logarithm tables