Author Archives: Jack Case

The ‘Where To Look’ Method.

Posted on May 5, 2015 by Jack Case

To determine the altitude and azimuth of a celestial body, we could make calculations by using mathematical formulae; we could compute them with the aid of sight reduction tables; we could use star globes and star charts or we could … Continue reading →

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Jupiter’s Retrograde Motion

Posted on April 8, 2015 by Jack Case

Jupiter moves across the sky in a very predictable pattern, but every now and then it reverses direction in the sky, making a tiny loop against the background stars – this is Jupiter in retrograde. The following diagram shows that, … Continue reading →

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Finding Stars and Constellations, Part IV

Posted on December 9, 2014 by Jack Case

This post continues the series Finding Stars and Constellations.     Boötes  The Herdsman   If we take a line from Alioth to Alkaid in the Great Bear and extend that line in an -imaginary curve for about roughly three hand-spans … Continue reading →

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Calculating Azimuth And Altitude At The Assumed Position By Spherical Trigonometry.

Posted on December 8, 2014 by Jack Case

There are several ways of calculating the azimuth and altitude at the assumed position; these include the use of sight reduction methods and software solutions. However, the traditional method is by the use of spherical trigonometry which is demonstrated below. … Continue reading →

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The Accuracy of Astro / Celestial Navigation

Posted on November 11, 2014 by Jack Case

 U.S. Navy and Royal Navy navigators are taught that the accuracy of astro navigation is ±1 minute of arc or 1 nautical mile and that where position lines are derived from astronomical observations, the resultant position is not known as a … Continue reading →

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Finding Stars and Constellations – Part III

Posted on November 8, 2014 by Jack Case

This post continues the series Finding Stars and Constellations. Lyra, Cygnus and Aquila – The Summer Triangle. The diagram below shows the constellations Lyra, Cygnus and Aquila. If we follow the reference line ‘the Pointers’ from Ursa Major to Polaris, … Continue reading →

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

Posted on October 31, 2014 by Jack Case

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

Posted on October 3, 2014 by Jack Case

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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Finding Stars and Constellations, Part I

Posted on August 2, 2014 by Jack Case

The usual practice for distinguishing the more conspicuous constellations is to establish reference lines in a known constellation and from these to memorize the directions in which other constellations lie on the celestial sphere. For example, one of the most well … Continue reading →

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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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