Tag Archives: navigation

What Is Sidereal Time

Posted on April 14, 2013 by Jack Case

Sidereal Time.  Even though Sidereal Time is a more accurate measure of the Earth’s rotation, we normally use Solar Time for time-keeping because the Sidereal Day is not a practical unit for us to use.  On the other hand, Sidereal … Continue reading →

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What Is The Mason Dixon Line

Posted on September 25, 2012 by Jack Case

Astro Navigation and the Mason Dixon Line Between 1763 and 1768, about 200 years before the advent of GPS, Charles Mason and Jeremiah Dixon marked the 233 mile long boundary line between Pennsylvania and Maryland and the 83 mile long … Continue reading →

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How To Locate The Pole Star (Polaris)

Posted on August 29, 2012 by Jack Case

First step – Look in the northern sky to find the constellation Ursa Major which is otherwise known as the Great Bear. Second step – find the Big Dipper (marked in red) which consists of the seven brightest stars of the constellation … Continue reading →

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The Southern Cross

Posted on August 29, 2012 by Jack Case

Just as we can use the Pole Star in the northern hemisphere to find the direction of north, we can use the Southern Cross in the southern hemisphere to find the direction of south.   However, whereas we can use the … Continue reading →

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The Rhumb Line

Posted on August 29, 2012 by Jack Case

If a ship were to steer a steady course, that is one on which her heading remains constant, her track would cut all meridians at the same angle, as the following diagram shows.  Such a line on the Earth’s surface … Continue reading →

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The Relationship Between Longitude, Latitude and the Nautical Mile.

Posted on August 29, 2012 by Jack Case

The Relationship Between Longitude and the Nautical Mile.  The Earth’s equatorial circumference is 21640.6 n.m.  Since the Equator is a great circle, 1o will subtend an arc of:  21640.6 ÷ 360 =  60.113  ≈ 60 n.m. There are 360 meridians of Longitude so … Continue reading →

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Calculating the Sun’s Declination in a Survival Situation

Posted on August 16, 2012 by Jack Case

In an ideal situation, we could find our latitude by using a satellite navigation system.  If sat-nav is not available, we can use astro navigation to calculate our latitude by the method shown at the following links: Latitude from the … Continue reading →

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Titanic and the Traverse Tables

Posted on January 8, 2012 by Jack Case

Recent discussions regarding the possibility that the SOS position sent by the Titanic was incorrect due to mistakes made in applying the traverse tables make interesting reading. Traverse tables have been used for about 200 years to solve the mathematical … Continue reading →

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Astro Navigation – What is it and why do we need it?

Posted on January 8, 2012 by Jack Case

Astro-navigation (or celestial navigation as it is also known) is a fascinating subject that encompasses many areas of knowledge including geography, astronomy, history and mathematics.  As you unravel the principles and techniques upon which navigation is based, you will be … Continue reading →

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Latitude from Polaris

Posted on January 8, 2012 by Jack Case

Using The Pole Star (Polaris)  To Find Your Latitude Assume that the Pole Star (Polaris)is exactly in line with the Earth’s axis produced, as shown in the following diagram. To an observer O on the Equator (lat. 0o) the Pole … Continue reading →

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