This page Nautical almanac on our self-instruction website emphasizes the significance of the nautical almanac as a crucial tool for celestial navigation.
And the nautical almanac is also used for the calculation of daylight hours and mandatory compass checks.
Significance of the Sumner Line:
Sumner’s method was revolutionary because it allowed navigators to determine a line of position rather than just latitude, improving accuracy.
It laid the foundation for modern celestial navigation techniques, including the Saint-Hilaire method, which is a more refined version developed later and used on this website.
The nautical almanac
I will only refer to the necessary tables for the sun.
Thus, I present some very simplified pages from the nautical almanac to make reading easier, solely for the main purpose of this site: calculating a line of position with the sun.
It should be noted that the nautical almanac is very dense and complete in a more universal context, including the planets, the moon, the stars, and all other useful tables for celestial navigation
In summary, the almanac mainly contains two different sections:
1. the daily pages and
2. the permanent tables.
Nautical almanac : daily pages
Declination (D) and Greenwich hour angle (GHA) of the sun in the nautical almanac
Firstly This publication gives for each day and each whole UT hour the Declination and GHA of the sun in the daily pages and it is up to us to interpolate and find the Declination and GHA to the nearest second.
Nautical almanac:
For example, in the Larochelle exercise, the Universal Time (UT) is 10 hours, 40 minutes, and 19 seconds.
daily page
sun
Also this daily page has been downloaded on the nauticalalmanac.it website with the kind permission of its author Capt. Roberto Iori.
For the whole hour 26/01/2022:
GHA at 10 hours = 326°52′,8
The Declination of the sun at 10 hours = 18°40′,1 S
The value of d is 0.6 ‘ (decreasing 0’,6 per hour.)
For the exact hour:
See increment of the sun’s hour angle
How to calculate sun’s Declination
Subsequently ( D ) and ( GHA ) are used with time (UT) in our mathematical formulas (solving the spherical triangle)
Nautical almanac:
permanent tables in the nautical almanac
Of course, these tables remain constant and are not updated annually like some other data in this publication
Increments and corrections tables:
Firstly, these increments tables show you the conversion time to arc
Indeed, the hour angle of the sun increases by 15 degrees every hour.
60 minutes → 15°
30 minutes → 7°30’
15 minutes → 3°45’
16 minutes and 7 seconds → 4° 01’,8 (see table below)
Furthermore, we find for each minute a table with 60 seconds.
The reason for these tables is that they can replace an electronic calculator.
sun only
Time to Arc:
TIME XX hour 16 minutes 07 seconds UT
→ ARC = 4° 01′.8
altitude corrections tables
Also, we will find a lot of explanations for the altitude correction tables in the interactive worksheet.
In fact, the french and english nautical almanacs use different methods for altitude corrections
Of course this is the english version
In addition the french nautical almanac
Éphémérides nautiques
(Bureau des Longitudes)
Moreover, the Greenwich Hour Angle (GHA) is commonly referred to as l’angle horaire du soleil (AHvo)
Also, see the french version of my french website (https://ladroitedehauteur.com)
