Table of Contents

Class Prep

Class 1
Class 2
Class 3
Class 4
Class 5
Class 6
Class 7
Class 8
Class 9
Class 10

>>Topical Articles<<
Assumed Longitude
Casio fx-260 Solar II
Emergency Navigation
Making a Kamal
Noon Sight
Pub. 249 Vol. 1
Sextant Adjustment
Sextant Skills
Sight Averaging
Sight Planning,
  Error Ellipses,
  & Cocked Hats
Slide Rules
Standard Terminology
Star Chart
The Raft Book
Worksheet Logic

Class 9:  September 5, 2019

New Pages Added to This Web Since Last Week

Class Plan

  • Quiz: Produce from memory the Big Dipper, and indicate the following stars:
    • Polaris
    • Dubhe
    • Alkaid
    • Arcturus
    • Spica
    • Regulus
    • Alphard

  • > Site Map > Celestial Navigation Data for Assumed Position and Time

  • Emergency Navigation: "Planning for the unexpected". Faraday Cage.

  • Emergency Navigation: You have no accurate watch.
    • Noon sights
    • Polaris sights

  • Emergency Navigation: You have no sextant.
    • Zero-altitude sun shots, either by Pub. 249 or by direct calculation1
    • Improvised kamal
      • Small kamal is accurate to 15' at altitudes up to 15°
      • Large kamal is accurate to 35' at altitudes up to 40°

Materials Required


Homework Assignment

  • Review the new and changed pages at this web site.


1 I have confirmed that you can definitely do zero altitude shots with the Bygrave equations. Where the celestial object is on the horizon, you can simply count on your Hc as being a negative number.

The equations don't clearly show this themselves since the values of tan(1°) and tan(-1°) are the same, given that slide rules never show negative values.

If you are doing a GC calculation of a distance between two points, there could be ambiguity as to whether the Hc is 89° away from you, or 91° away.

But with a celestial sight, it will be unambiguous since you can see with your eyes that the LL or UL of the sun/other celestial object is on the horizon...which means the actual altitude of the center of the sun is negative.

The further north you are, the more likely you are to have a MA > 90°, even if the actual distance between you and the destination is less than Hc = 90°. So MA is no guide to whether values are negative or not.

The safest bet when doing GC course-and-distance calculations by slide rule is to never try and calculate a distance greater than 1/4 the circumference of the earth.

When using the same equations with celestial sights, it will be rare to have Hc altitudes less than 0°...and really the only scenario is the zero-altitude shot. [Return]