9: Instruments Used in Celestial Navigation

1. 9: Instruments Used in Celestial Navigation Presented By: MATE O

2. Course Outline • Navigational Astronomy Lecture 1 & 2 • Mean Time / Apparent Time Lecture 3 • Time Zones, Zone Description, Chronometer Time Lecture 4 • The Earth, Celestial, And Horizon Coordinate System Lecture 5 & 6 • The Spherical Triangle Lecture 7 • Circle of Equal Altitude Intercept Lecture 8 • Time Diagram, Right Ascension Lecture 9 • The Nautical Almanac, Finding GHA, LHA, and Dec. Lecture 10 & 11 • Instruments For Celestial Navigation Lecture 12 • Sight Reduction of the Sun, Stars, Planets, Moon Lecture 13 - 15 • Plotting and Advancing / Retarding the Assumed Position Lecture 16 • Calculating Time of Meridian Passage (LAN) Lecture 17 • Calculating Latitude at Meridian Passage Lecture 18 • Calculating Time of Sunrise/ Sunset/ Twilight Lecture 19 • Star Shooting Schedule / Pub. 249 Lecture 20 • Azimuth and Amplitudes Lecture 21 – 24 • Polaris – Azimuth and Latitude By Lecture 25 • Star – Finder – Stars, Planets, Selecting the 3 best Stars Lecture 26 • The Complete Day’s Work Lecture 27 & 28

3. The Marine Sextant IX: Instruments For Celestial Navigation Parts Frame Limb Graduated Arc Index Arm Tangent Screw Release Clamp Micrometer Drum Vernier Index Mirror Horizon Glass Shade Glasses Telescope Handle

4. < BGC = ½ < ADC Optical Principle Of A Sextant IX: Instruments For Celestial Navigation A Ray of Light That Has Undergone Two Reflections in the Same Plane Is Twice the Angle the Two Reflecting Surfaces Make With Each Other. Example: If a Star Is 60° Above the Horizon < ADC = 60° Then < BGC = 30°However, the Graduated Arc Is Labeled With 60° (The Actual < Above the Horizon)

5. The Marine Sextant IX: Instruments For Celestial Navigation

6. Care of the Sextant IX: Instruments For Celestial Navigation • Always Keep Sextant in Its Case, Secure at Sea When Not in Use • If You Must Set It Down, Set It on Its Legs - - Never on Its Mirrors • Do Not Drop the Sextant • Keep It Moisture Free (Use Silica Gel Inside the Case) • Keep Mirrors and Arc Clear of Debris, Wiping the Mirrors With Lens Paper and a Small Amount of Alcohol • If Sea Water Spray Gets on the Sextant, Rinse With Fresh Water and Dry Gently With a Soft Cotton Cloth or Lens Paper • Use Light Pressure When Cleaning • Occasionally Oil and Clean the Tangent Screw and Teeth on the Side of the Limb • When Stowing for Long Periods Use a Thin Coat of Petroleum Jelly to Protect the Arc • If the Mirrors Need Re-Silvering Take the Sextant to a Sextant Repair Shop

7. Adjustable Errors of the Sextant IX: Instruments For Celestial Navigation Prismatic Error Graduation Error Centering Error Non-Adjustable Perpendicularity Error Side Error Collimation Error Index Error

8. Testing For Perpendicularity Error IX: Instruments For Celestial Navigation

9. Testing For Side Error IX: Instruments For Celestial Navigation Glass Mirrored Glass Mirrored No Side Error Side Error

10. Alternative Method IX: Instruments For Celestial Navigation Glass Glass Mirror Mirror Horizon Horizon No Side Error Side Error Exists

11. Collimation Error IX: Instruments For Celestial Navigation Testing For Error Of Collimation Bring Two Stars 90° or More Apart, Together In View Tilt Sextant to See If They Remain “in coincidence”

12. Index Error IX: Instruments For Celestial Navigation Horizon Horizon Horizon Horizon Index Error Exists Turn Micrometer Drum Slowly Until Horizons Line Up. Your Sextants’ Distance From 0° 00’ Will Be Your Index Error On Or Off The Arc Hold The Sextant Vertically With Sextant Set at 0°

13. Reading the Sextant IX: Instruments For Celestial Navigation Hs = 29° 42.5’

14. Reading the Sextant IX: Instruments For Celestial Navigation

15. IX: Instruments For Celestial Navigation Reading the Sextant

16. Reading the Sextant IX: Instruments For Celestial Navigation

17. Taking the Sight IX: Instruments For Celestial Navigation • Sun - Shade Glasses • Moon – Limb to Choose • Swinging The Arc (Ensuring You are Tangent To Horizon) • Importance of Accurate Time • Back Sights • False Horizons • Abnormal Refraction (Dip)

18. Taking the Sight IX: Instruments For Celestial Navigation • Three Methods of Observing a Celestial Body • Bringing the Celestial Body to the Horizon • Holding the Sextant Upside Down, Bring the Horizon to the Body • Determine in Advance the Altitude and Azimuth of the Body and Face in the Direction of the Azimuth. The Body Should Be Near the Predicted Altitude.

19. Taking the Sight IX: Instruments For Celestial Navigation

20. Taking the Sight IX: Instruments For Celestial Navigation

21. Taking the Sight IX: Instruments For Celestial Navigation • When Using The Sextant We Must Take Into Account The Difference Between The Celestial Horizon And The Visible Horizon Due To Our Height Of Eye. • This Is Known As The Dip Correction And Is Applied To Sextant Altitude To Obtain Apparent Altitude (Ha)

22. Vega 0530 SPICA Arcturus 0530 0530 Selecting Stars To Observe IX: Instruments For Celestial Navigation Choose the Stars And/or Planets That Will Give the Best Bearing Spread (See Example Below) Select Bodies With a Predicted Altitude Between 20° and 70° Observe the Bodies in the East First in the MorningObserve the Bodies in the West First in the Evening Take Sights of Brightest Stars First in the EveningTake Sights of Brightest Stars Last in the Morning Predict Expected Altitudes for up to 7 Celestial Bodies When Preparing to Take Celestial Sights

23. Exact Time IX: Instruments For Celestial Navigation Exact Time - Accuracy of Recording the Time Is of Utmost Importance • Use an Assistant to “Mark” the Exact Time You Observed the Body • Or, Note the Time As Quickly As Possible After Shooting the Body (Deducting Any Seconds It Took to Look at Your Watch) • Failure to Obtain Accurate Time Will Result in Large Errors in Your Work

24. The Marine Chronometer IX: Instruments For Celestial Navigation The Marine Chronometer is a Precision Time Piece Used Aboard a Ship to Provide Accurate Time for Celestial Observations Knowing and Maintaining a Record of the Chronometer Error Can Determine a Chronometer Rate, Which Will Allow the Navigator to Calculate What Exact GMT Should Be on Any Given Day Chronometer Error Should Be Checked Once a Day Against an Accurate Time Source Such As a Time Tick on a Radio

25. Checking Compass Error IX: Instruments For Celestial Navigation • A Compass May Be Checked For Accuracy Using Celestial Bodies By Comparing An Observed Compass Bearing Of The Celestial Body With A True Bearing Calculated Using Celestial Navigation Procedures • The Two Most Common Ways Of Checking A Compass Using Celestial Bodies Are By Azimuths And Amplitudes • Common Equipment Used To Observe Azimuths And Amplitudes • The Azimuth Circle – A Ring Designed To Fit Snugly Over A Compass Repeater To Allow For Compass Bearings Or Azimuths To Be Taken • The Alidade – A Bearing Circle Fitted With A Telescope To Assist In Taking Bearings