# Captain Jack's Celestial Navigation / Edition 1

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### Overview

Captain Jack I. Davis has done it again! He has written yet another, very easy to understand, instructional navigation book. As in his first book, Captain Jack's Basic Navigation, this book is filled with knowledge, new sea stories, and more humorous anecdotes.

Using the same highly successful format of his first book, Captain Jack takes the reader through each phase of navigation by first explaining, in detail, the steps needed to complete each phase. This is followed by a list of questions to answer, using your new-found knowledge. After you have completed the questions, you can check your answers at the end of each chapter. All the calculations are accomplished with simple, grade school math using an inexpensive calculator and basic plotting tools.

If you believe you do not need these Old Time navigational skills in this modern age of electronic navigation, Captain Jack restates his suggestion to you: "Tape a mirror below your GPS display. When the electronics fail, you can look in the mirror and see exactly who is lost."

### Product Details

• ISBN-13: 9781892216182
• Publisher: NetPV
• Publication date: 1/1/1999
• Edition description: Comb Bound
• Edition number: 1
• Pages: 152
• Product dimensions: 5.50 (w) x 8.50 (h) x 0.35 (d)

From Chapter 1:
The sextant will measure the height above the horizon of a celestial object, (sun, moon, planet or star), in degrees, minutes and fractions of a minute. Some sextants show seconds instead of a fraction of a minute.
What good is this to us? How does this help us find our position? To demonstrate, let's look at Polaris, the North Star.

Our latitude in Southeast Texas is about 30 degrees North. When we use our sextant to shoot a sight of Polaris we face north and find the star is about 30 degrees above the horizon. If we were in Nebraska, our latitude would be about 45 degrees North and facing north our sextant would show Polaris to be 45 degrees above the horizon. In fact if we move all the way north to the North Pole we would be at 90 degrees North latitude and our sextant would read 90 degrees height for Polaris, regardless of which direction we faced.

Therefore, we can determine our latitude by measuring the altitude of Polaris.

We can determine the distance we are away from the North Pole, by measuring the height of Polaris. The point directly below a celestial object is called the GP. The GP of Polaris "wobbles" around the North Pole every twenty-four hours, so a sextant reading at dusk will be slightly off, as will a morning reading. An average of the two readings will be exact since the morning error and the evening error offset. The nautical almanac gives corrections for both.

POLARIS
How to find it
EQUATOR TO POLE

If a sextant reading is 30 degrees, subtract that from 90 degrees, which gives the co-altitude of Polaris. In this example, that would be 60 degrees. Since each degree is equal to 60 nautical miles distance, 60 degrees times 60 miles equals 3600 miles, the distance from the North Pole.
Co-altitude x 60 miles = 3D distance away.

Figure 1-1 Jack Davis

The early ocean navigators understood that you could find your latitude using the North Star.

They didn't have the very accurate sextants we have today. They had a crude instrument called an astrolabe, which would give them a rough reading. When Columbus discovered the entrance to San Juan Harbor, Puerto Rico, he knew (from the astrolabe) the entrance was at about 19 degrees North latitude. He didn't have a clue what his longitude was and for his purposes it didn't matter.

When he sailed back toward his home port, he sailed north until he arrived at the latitude of the Mediterranean entrance. There, he turned east and ran that latitude line until the Rock of Gibraltar came into view.

On his return trip to San Juan, he sailed from the Mediterranean, past the Rock of Gibraltar and sailed south to 19 degrees North. He followed that latitude line until Puerto Rico came into view.
The thousands of sailors who followed in Columbus's wake, said when leaving the
Mediterranean to go to the West Indies, you sail south until the butter melts, then turn right.

This "latitude sailing" has been used by sailors (and aviators) well into the electronic age and in fact I still use the technique on occasion.

INTRODUCTION
CHAPTER ONE: THE SEXTANT
What it does and how to use it.
CHAPTER TWO: NAUTICAL ALMANAC
The inside front cover - Ho to Hc
CHAPTER THREE: GP and the DAILY PAGES
CHAPTER FOUR: LHA
Assumed Position, Pub 249
CHAPTER FIVE: STARS AND PLANETS
CHAPTER SIX: STAR FINDERS
CHAPTER SEVEN: THE MOON
CHAPTER EIGHT: THE NOON SIGHT
CHAPTER NINE: EXERCISES
BOAT DELIVERIES
PREFACE
RIGGING PROBLEMS
ISLA MUJERES, MEXICAO
THE MAKING OF A FISHERMAN
CLEAN FUEL
CENTERBOARD NIGHTMARE
"COME BACK" LITTLE TEXACO
APPENDIX ONE NAUTICAL ALMANAC
GLOSSARY OF BOATING TERMS
AVAILABLE BOOKS

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