Nautical almanac and sumner line

This page Nautical almanac and sumner line on our self-instruction website emphasizes the significance of the nautical almanac as a crucial tool for celestial navigation. It assists mariners in accurately determining their position using the Sumner line of position or line of position de St Marcq Hilaire while navigating the open sea.

And the nautical almanac is also used for the calculation of daylight hours and mandatory compass checks.

I will only refer to the necessary tables for the sun.

Nautical almanac and sumner line, daily page nautical almanac (sun only)
daily page nautical almanac (sun only)
This is a used Freezer Trawler.  author image: Bob at workboats USA
Nautical almanac and sumner line, image of the almanac
Her Majesty’s Nautical Office U.K. and Nautical Almanac Office U.S.

Greenwich hour angle (GHA)

Declination (D)

Nautical almanac and sumner line,image point PG

While a thread stretched between the Sun center and the Earth center strikes the Earth’s crust at the point PG

Nautical almanac and sumner line: Declination (D) and Greenwich hour angle (GHA)

Declination (D) and Greenwich hour angle (GHA) in the nautical almanac

Firstly This publication gives for each day and each whole UT hour the Declination and GHA in the daily pages and it is up to us to interpolate and find the declination and GHA to the nearest second.

Nautical almanac and sumner line:

For example, in the Larochelle exercise, the Universal Time (UT) is 10 hours, 40 minutes, and 19 seconds.

Nautical almanac , image watch ut time
watch on UT time. Wednesday, January 26th.

daily page


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 explanation in the interactive worksheet

Also this daily page has been downloaded on the website with the kind permission of its author Capt. Roberto Iori. You can also look at the link page

Subsequently ( D ) and ( GHA ) are used with time (UT) in our mathematical formulas (solving the spherical triangle)

beach : La Lette blanche dans les Landes en France. Author image: VIGNA Christian

Nautical almanac and sumner line:

permanent tables in the nautical almanac

These tables remain constant and are not updated annually like some other data in this publication

Increments and corrections tables:

These increments tables show you the conversion time to arc

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)

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

Nautical almanac increment and corrections tables
Increments and corrections tables

Time to Arc:

TIME xx hour 16 minutes 07 seconds UT

As a result the ARC = 4° 01′.8

Denham Western Australia… Author image: Murray Foubister

permanent tables in the nautical almanac:

altitude corrections tables

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
the french nautical almanac

Éphémérides nautiques 

(Bureau des Longitudes)

Also, the Greenwich Hour Angle (GHA) is commonly referred to as l’angle horaire du soleil (AHvo)

See the french version of my french website (