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 7:  August 22, 2019

New Pages Added to This Web Since Last Week

  • Developing Your Sextant Skills: three paragraphs added at the top of the page.
  • An addendum has been added to the section on Pub. 249 in the Pre-Class Prep.

    Note that direct calculation is faster than Pub. 229, and delivers as much accuracy as you can possibly get, when done with an electronic calculator.

Class Plan

  • Quiz: Produce from memory the Orion asterism, and indicate the following stars:
    • Betelgeuse
    • Rigel
    • Aldebaran
    • Capella
    • Pollux
    • Procyon
    • Sirius
  • Reduce Ofer's Arcturus shot by slide rule, and plot
  • Revisit sight averaging, using Pub. 249.

    A giant asteroid has produced a freak eclipse of the sun. For the time being, stars are visible in the sky. We know that when the asteroid hits the earth, all life will be extinguished. In the minutes that remain to us, we take a star sight, savouring the idea of taking a star sight during the daytime.

    DR:     53° 30.3' North, 113° 38.5' West
    Object: Regulus
    Date:   August 19, 2019
    Watch:  3 Seconds Fast
    Time:   17:05:26 MDT     Hs: 33° 32.0'
    Time:   17:06:15 MDT     Hs: 33° 28.3'
    Time:   17:06:54 MDT     Hs: 33° 23.1'
    Time:   17:07:44 MDT     Hs: 33° 21.3'

    Determine the best sight to use and complete the sight reduction and plotting.

Range of Ofer's Slide Rule

Tangents from 5.71° to 89.43°
Cosines from 0.00° to 84.26°

T + C:  Tan 0.1 → 1.0 = 5.71° → 45.00°
T + CI: tan 100 ← 1.0 = 89.43° ← 45.00°
S:      cos 0.1 ← 1.0 = 84.26° ← 0.00°

(Next week, we will use a mock-up of the Mark 1 slide rule and observe how it works to solve the same sort of problems.)

Materials Required

  • Sight reduction worksheet, designed for direct calculation
  • Sight reduction worksheet, designed for use with Pub. 249
  • Israel plotting sheet
  • Universal Plotting sheet


Homework Assignment

  • Review the new and changed pages at this web site.
  • Finish reducing the first Arcturus sight by slide rule. Plot it.
  • Reduce the second Arcturus sight by slide rule. Plot it if the results are significantly different from the first sight.
  • Reduce the first Arcturus sight using Pub. 249. Plot it.
  • Download paper mock-up version of Mark 1 Navigator's Slide rule
    • Cut out, and tape to a piece of cardboard.
    • We will use this sometime in the next class or two.