Tag Archives: astronomy

The Demystified Astro Navigation Course – Unit 3 Part 1

Unit 3  Part 1 – Altitude and Azimuth     The Azimuth is similar to the bearing in that it is the angle between the observer’s meridian and the direction of the celestial body.  However, whereas bearings are measured clockwise from north … Continue reading

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The Demystified Astro Navigation Course Unit 2

Unit 2 – Local Hour Angle and Greenwich Hour Angle  Local Hour Angle (LHA).  In astro navigation, we need to know the position of a celestial body relative to our own position. (The following diagram illustrates the explanations given below). LHA … Continue reading

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The Demystified Astro Navigation Course – Unit 1

Unit 1 Essential Astronomy for Navigators The Celestial Sphere is an imaginary sphere with the Earth located at its centre. We imagine that the ‘celestial bodies’ such as the Sun, Moon, stars and planets are placed on the inner surface … Continue reading

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Altitude Correction for Semi-Diameter

An adjustment for semi-diameter is one of the corrections that may have to be made to the sextant altitude in order to calculate the True Altitude.  Corrections For The Moon’s Semi-Diameter.  The point on the Moon’s circumference nearest to the … Continue reading

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The ‘Where To Look’ Method.

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

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

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.

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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Finding Stars and Constellations, Part I

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.

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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