Celestial Navigation Example

Silicon Sea, leg 57

In these web pages, I will show an example of celestial navigation, step-by step. I have chosen as my example the sample leg 57 from the sample problem series Silicon Sea

In this sample problem, we start with a boat whose last known position was 51°30.0'S, 80°59.5'W. We have the boat's heading and speed, and the current. After nearly a day of sailing, we take sextant sights on the moon and four stars. The goal of the exercise is to determine the boat's current position.


For the purposes of this exercise, we need the following items:

If you don't have the 1999 Almanac handy, you can visit Omar Reis's awesome web-based almanac or the U.S. Navy's online almanac.

For more resources, see http://www.celestialnavigation.net/


There are several steps to solving for our current position. Each is handled on its own page:
  1. Use dead reckoning to estimate current position
  2. Prepare a plotting sheet
  3. Compute line of position for Rigil Kentaurus
  4. Compute line of position for Acrux
  5. Compute line of position for Aldebaran
  6. Compute line of position for Peacock
  7. Compute line of position for the Moon
  8. Final plot
  9. Answering the questions in the exercise
  10. Addendum — solving with calculator instead of tables
  11. Addendum — The Lunar Method
  12. Addendum — Glossary


See the excellent page at celestialnavigation.net for more resources.

Bowditch -The American Practical Navigator is the textbook on navigation. It can be found online at irbs.com. Google also has scans of older editions of Bowditch on line: 1821, 1826, 1906

Other sources:

Nga.mil: 2002 edition, Wikisource: HTML formated version.

Government charts for air navigation can be found at nga.mil. These charts are in a different format from marine charts and are optimized for rapid computations.

Papers on celestial navigation algorithms. (Note: plagiarizes one of the diagrams from this web site.

The Vietnam Maritime Social Network has a large number of excellent articles on celestial navigation.

H. Umland's Freeware Page

Java Script Programs for Navigators by Jacky Wong

Omar Reis's Online Nautical Almanac

Omar Reis's Navigator Light Computer Program

W. Fendt's Apparent Position of a Star Astronomy Java Page

W. Fendt's Coordinate Graphic (Celestial Poles) Java Page

Almanac and Sight reduction Information from the Navy

Pocket Stars — Integrated Star Chart, Ephemeris, and Celestial Navigation Software for the Pocket PC.

ASNAv — "designed by a seaman for seamen."

Sailing Alone Around the World, by Captain Joshua Slocum.