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GPS Backup with a Mark 3 Sextant



Background Article on our Modern Regiment of the North Star

Video illustrating the process.

Expanded Tables (to remove or minimize interpolation)

Practice with Dec and GHA

PRACTICE Finding sun's declination using the Backup Sun Almanac

PRACTICE Finding Sun's GHA using the Backup Sun Almanac

Finding UTC of LAN

Finding UTC of LAN using the Starpath Custom Sun Almanac

Finding UTC of LAN using an Analemma 

Hi-res analemma graphic

Arc to Time Table

PRACTICE Finding UTC and WT of LAN

Miscellaneous related articles

Accuracy of Back up Cel Nav Using a Mark 3

Progress to Weather ... a topic that comes up in some exercises that use this book

The book mentions putting together a backup kit made up of this book, a Mark 3 sextant, and a rated watch. We have such a kit availabe which includes all other aids needed to for ocean navigation. See contents at Starpath GPS backup kit.


PRACTICE with Latitude by Polaris

Example 1: With the sky below...

July 19, 2021, UTC = 05:56:28
DR: 44N, 141W
Hs Polaris = 43° 23.4'
What is your latitude? Solution 1


Example 2:  with the sky below...

July 14, 2020, UTC = 14:42:44
DR: 25N, 151W
Hs Polaris = 25° 29.4'
Find your latitude. Solution 2



This book is now in the 7th printing. Earlier printings had several typos including these two


Page 4, Figure 2-2, Insert should look like:

Page 17. Table 5-2, Lat should be 35° 80,6' (36° 20,6'). Error source earlier in the table: Ho = 75° 14,0', not 74° 14,0'.