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 altitude using only logarithm tables, without the necessity of a scientific calculator.
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
The formula
L = Dead reckoning latitude
D = Declination of the sun
P = polar angle
Explanation of the versine
versine P = (1− cos P)
log(versine P) = log(1− cos P)
Table 2 provides the values of the versine directly.
Explanation of (L±D)
See page: SAME NAME/NOT SAME NAME, which is part of the logarithm method. In this section, we do not use the rule of signs.
Ancestral celestial Douwes formula:
Explanation of Table 4
Finally, after having found log 2nd Term, we will seek with the help of table 4 (logarithms of whole numbers) the natural 2nd Term (antilog)
Explanation of Table 5
Consequently, from the result cos (L±D) − 2nd natural Term = sin Hc, we obtain 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.
example Hc with the logarithm tables
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
You can also find a short description of the sextant’s history on these page links and other helpful resources.
On the webpage Links and Helpful Resources, you can find a short history of the sextant.