Category Archives: astronomy

The Importance of Azimuth and Altitude in Astro Navigation

 In the diagram above, the celestial sphere is drawn in the plane of the observer’s meridian with the observer’s zenith (Z) at the top.  Point O represents both the observer and the Earth. Z represents the observer’s zenith. X is … Continue reading

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Bearing, Azimuth and Azimuth Angle.

For students of astro navigation, the various definitions of azimuth, azimuth angle and bearing can cause much confusion. It is hoped that the following will help to clarify this topic. Bearing is the direction of something in relation to a … Continue reading

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Pillars of the Sky (Learning from the Polynesians).

The last post in this series discussed the Polynesian’s Star Compass and their use of ‘steering stars’ for direction finding.  Although the Polynesians made extensive use of a form of dead reckoning to estimate position, as far as we know, … Continue reading

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The Polynesian Star Compass (Learning from the Polynesians)

Updated version. “Know the stars and you will always have a compass”  (The Revenant) * Nainoa Thompson tells us how that, for centuries before European sailors reached the Pacific Ocean, the South Sea Islanders accurately found their way from island … Continue reading

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Astro Navigation In A Nutshell Part 1

Part 1 – The Importance of Azimuth and Altitude.  The theory of astro navigation depends on the ability to solve the spherical triangle PZX in the diagram below.  The azimuth and altitude enable us to calculate the Local Hour Angle … Continue reading

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Astro Navigation In A Nutshell Part 2.

Part 2 – The Intercept Method Link:  Astro Navigation In A Nutshell Part One Suppose we are in a yacht and we measure the altitude of the Sun and find it to be 35o; what does this tell us?  All … Continue reading

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Astro Navigation in a Nutshell Part 3

Part 3 – Calculating Altitude and Azimuth at the Assumed Position by Spherical Trigonometry. Links:  Astro Navigation In A Nutshell Part One Astro Navigation In A Nutshell Part Two There are several ways of calculating the azimuth and altitude at the … Continue reading

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Applying the Equation of Time when calculating longitude at the Sun’s Meridian Passage.

Author’s Note:  The original issue of this post was found to contain errors which have now been corrected.  Many thanks to Jeremy Parker for bringing the errors to my attention. Although the imaginary Mean Time gives us an accurate measurement … Continue reading

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Meridian Passage Long Method

Links:  Understanding Meridian Passage, Equation of Time,   Meridian Passage Short Method,  Short Distance Sailing Formulae,  What is the point of meridian passage?         Zone Time,    Local Hour Angle and Greenwich Hour Angle,   Converting GMT to GHA … Continue reading

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Understanding Meridian Passage (Mer Pas)

Meridian Passage occurs when a celestial body crosses the observer’s meridian of longitude and at that instant, it will reach its greatest altitude above the observer’s horizon. The following diagrams will help to explain how the latitude can be calculated from the … Continue reading

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