Category Archives: Uncategorized

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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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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