Tag Archives: astro navigation

Rising and Setting Times of Stars.

Posted on June 9, 2014 by Jack Case

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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Survival – Calculating Altitude Without An Angle Measuring Instrument

Posted on April 4, 2014 by Jack Case

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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Zone Time

Posted on November 22, 2013 by Jack Case

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

Posted on November 9, 2013 by Jack Case

  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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The Intercept Method

Posted on November 8, 2013 by Jack Case

Although it is usual these days to calculate an observed position in astro navigation by using the Rapid Reduction Method, there are other methods which do not necessitate the purchase of expensive reduction tables.  One of these methods is the … Continue reading →

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How To Find Longitude

Posted on September 3, 2013 by Jack Case

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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What are Local Hour Angle and Greenwich Hour Angle

Posted on August 17, 2013 by Jack Case

Local Hour Angle (LHA). In astro navigation, we need to know the position of a celestial body relative to our own position. In the diagram below: LHA is the angle BNU on the Earth’s surface which corresponds to the angle ZPX … Continue reading →

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What are Azimuth and Altitude

Posted on July 22, 2013 by Jack Case

Azimuth and Altitude part 1 We can define the position of a celestial body in relation to its local hour angle and declination.  We can also state its position in relation to our own celestial meridian and celestial horizon; in … Continue reading →

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Keeping Time By The Sun

Posted on May 24, 2013 by Jack Case

The True Sun.  Life on Earth is governed by the movement of the True Sun; that is the sun we see in the sky and not by the theoretical Mean Sun.  The units of time in everyday use are defined … Continue reading →

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Is Venus an Evening Star or a Morning Star?

Posted on May 16, 2013 by Jack Case

Venus sometimes appears as an evening star above the western horizon shortly after sunset and sometimes appears as a morning star above the eastern horizon shortly before sunrise.  In primitive times, people regarded the evening and morning stars as two … Continue reading →

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