Category Archives: Uncategorized

What’s The Point Of Calculating Our Latitude From The Altitude Of The Sun At Midday?

Referring to my earlier post ‘Calculating Latitude from the Midday Altitude of the Sun’, the question has been raised “what is the point of this if you already know your latitude”?  The answer to this question is quite simple, if … Continue reading

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Finding Stars and Constellations Part II

Continuing the series ‘Finding Stars and Constellations’ Cassiopeia.  This constellation is named after the vain queen Cassiopeia in Greek mythology. The five stars in the constellation Cassiopeia appear in the celestial sphere in the shape of the letter W and can … Continue reading

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Rising and Setting Times of Stars.

It is very useful to be able to calculate the times at which the principal stars and constellations will rise in the east.  It is also helpful to be able to predict the approximate position of the star or constellation … Continue reading

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Distance To The Horizon

Pythagoras provides us with a method calculating the distance to the horizon. In the diagram below, A represents a ship’s position. B is the top of the lighthouse. B1 is the base of the lighthouse. C is the Earth’s centre. r … Continue reading

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Survival – Calculating Altitude Without An Angle Measuring Instrument

Links:  Astro Navigation in a survival situation.    Latitude from the midday Sun.    Find your longitude.     Calculating declination.    Declination table.     Trig table.    Revise trigonometry  Revise Spherical Trigonometry As the above links demonstrate, there are several methods of employing astro navigation … Continue reading

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The Relationship Between Altitude and Zenith Distance

Several readers have raised questions relating to my post dealing with the Intercept Method.  These questions mostly concern the relationship between altitude and zenith distance and also the relationship between angular distance and the nautical mile. Since several chapters of … Continue reading

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Zone Time

It would be impossible for a ship at sea to keep to the time of its longitude because (unless it is travelling due north or south) the longitude will be constantly changing.  For this reason, the sea areas of the … Continue reading

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Lunar Distance

  With the invention of the chronometer in 1759, mariners were, for the first time, able to calculate longitude by finding the difference between Greenwich Mean Time and Local Time.  However, the marine chronometer did not become affordable until around … Continue reading

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Rhumb Line Sailing

Terminology.  The following terms are used in this exercise:  Rhumb Line, Departure, D.Long, D.Lat, Mean Lat,      Mid. Lat.To find the meaning of these terms, click here:    Short distance sailing is a term which is applied to sailing along a … Continue reading

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How To Find Longitude

The longitude problem.  The measurement of longitude was a problem  until well into the 18th. century.  Determining latitude was relatively easy because it could be calculated from the altitude of the sun at noon but for longitude, early navigators had to rely on dead … Continue reading

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