Principles of Celestial Navigation

Supplemental Material » Determining Hc and Zn Using the Publications » Interpolation is Required to Use The Nautical Almanac

This sounds easy, and it is. However, both books involve tables, and therefore we must interpolate between table entries. For example, The Nautical Almanac gives the position of the Sun every hour throughout the year.

page from Nautical Almanac showing Sun positions with time of day

Because we normally do not observe an object exactly on the hour, we must interpolate between tabulated hourly entries. The interpolations are not difficult; strip forms and other tables in the book can be used to guide you.

Interpolation (Increments and Corrections) table from the Nautical Almanac. These tables help account for differences in celestial coordinates at second intervals.