# Category Archives: Astro Navigation Topics

## The Demystified Astro Navigation Course Unit 6

UNIT 6 –  Calculating zenith distance and azimuth at assumed position. We can use sight reduction tables to calculate the zenith distance and azimuth at the assumed position or else we can use the traditional method of making the calculations … Continue reading

## 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

## Calculating the Distance Between Meridians of Longitude Along a Parallel of Latitude.

At the Equator, the distance between meridians of longitude is 60 n.m. (or 60.113 to be precise).  However, as we move north or south away from the equator, we find that the distance between them decreases as they converge towards … Continue reading

## Altitude Correction for Parallax

As shown in the following diagram, the observer measures the altitude in relation to the visible horizon from his position at O on the Earth’s surface.  So, the observed altitude is the angle HOX.  However, the true altitude is measured from the … Continue reading

## Altitude Correction for Dip

Dip.  A correction has to be made to the sextant altitude to allow for the height of the observer’s eye above the horizon; this is known as Dip. Consider the diagram below: O is an observer’s position on the Earth’s … Continue reading

## 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

## Converting GMT To GHA

Greenwich Mean Time (GMT) is the local mean time anywhere on the meridian of Greenwich.  In other words it is the Local Hour Angle of the Mean Sun on the meridian of Greenwich. Since the Greenwich meridian is used as the … Continue reading

## 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