Principles of Celestial Navigation

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  Launch Quiz

  Published on: 2015-04-23
  Estimated time to complete: 2.00 - 3.00 h
  Includes audio: yes

  Topic Area(s)

  Geospatial
  Oceanography/Marine/Tsunami
  

  Description:

  This lesson provides a basic introduction to celestial navigation for navigators, sailors, and others interested in the topic. It begins with the relationship between celestial coordinates and Earth coordinates and examines key celestial navigation parameters—geographic position, sextant altitude, observed altitude, azimuth, and computed altitude—that can be used to identify to a ship's position. A U.S. Navy navigator demonstrates the main celestial sights performed over the course of a day, including the morning three-star fix, morning Sun line, Local Apparent Noon Sun line, afternoon Sun line, and evening three-star fix, and demonstrates how the sight reduction culminates in a marked intercept and line of position on a navigation plot. The concepts of fix, running fix, estimated position, dead reckoning, and assumed position are also discussed. Although no formal background is needed for this lesson, some familiarity with the basics of navigation and the Universal Plotting Sheet will be useful to the learner.

  Objectives:

  
  
  1. 
     Name the coordinates that define a location on Earth, a location on the sky, and a location as viewed from the rotating Earth.
  
  
  2. Define "geographic position" with respect to the position of a celestial object.
     
  
  
  3. Define zenith and zenith distance.
     
  
  
  4. Describe how one measures zenith distance.
     
  
  
  5. Describe the relationship between zenith distance and geographic position.
  
  
  6. 
     Define lines of position (LOPs), and what intersecting LOPs determine.
  
  
  7. 
     List the steps that a navigator performs as he/she plots lines of position; describe how to plot LOPs on a chart.
  
  
  8. 
     Summarize the accuracy of positions determined using celestial navigation.
  
  
  9. 
     List some advantages and limitations of celestial navigation.
  
  
  10. 
      List the information required to obtain a celestial navigation fix.
  
  
  11. 
      List the instruments required to make an observation.
  
  
  12. 
      List the necessary corrections to a sextant measurement, also known as sextant alitude or Hs, to produce an observed altitude or Ho.
  
  
  13. 
      Describe the Intercept Method.
  
  
  14. 
      Describe why an "assumed position" is used.
  
  
  15. 
      Describe how to calculate the intercept distance using Ho and Hc.
  
  
  16. 
      Describe how the intercept distance, azimuth, and the moniker HoMoTo are used to plot a LOP.
  
  
  17. 
      Describe the special publications used to determine Hc and Zn of an object.
  
  
  18. 
      Describe the contents of The Nautical Almanac and Pub 249, and how they are used in sight planning.
  
  
  19. 
      List the different navigational sights taken during a 24-hour period on a naval passage.
  
  
  20. 
      Define the concept of a running fix and explain how to plot it.
  
  
  21. 
      Describe how mid-morning and mid-afternoon sun sights can constrain a running fix.
  
  
  22. 
      Summarize the concept of a Local Apparent Noon Sun sight, and how it can yield a fix.
  
  
  
  

  Keywords

  Earth, coordinates, celestial sphere, latitude, longitude, declination, Greenwich Hour Angle, GHA, equator, meridian, degree, minute, nautical mile, geographic position, altitude, azimuth, sextant, index correction, dip, star, navigation, Sun, morning, evening, sight, Local Apparent Noon, LAN, fix, running fix, estimated position, dead reckoning, assumed position, Nautical Almanac, celestial data calculator, Ho, Hc, Hs, Zn, ship, position, sight reduction, intercept method, altitude-intercept method, Marcq Saint Hillaire Method, Universal Plotting Sheet, line of position, LOP