Author Archives: Jack Case

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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How To Make A Survival Sundial

Posted on May 8, 2013 by Jack Case

Calculating Time In A Survival Situation         How To Make A Sundial Relevant  Links:   Astro Navigation in a Survival Situation, Equation of Time ,  Sidereal Time Suppose you are shipwrecked on the Skeleton Coast of Namibia or you are … Continue reading →

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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 Equation of Time

Posted on April 6, 2013 by Jack Case

The Sun as a Time-Keeper.  Because the Earth’s orbital motion is not uniform, there are corresponding variations in the apparent speed of the Sun as it travels round the earth.   For this reason, the true Sun (the Sun that we … 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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