# Category Archives: Schools

Mars We can best understand  the retrograde and prograde motions of Mars by considering the planet’s motion relevant to distant stars.  To do this, we must study the effect of the motions of both the Earth and Mars around the … Continue reading

## Making An Ocean Plotting Sheet

Ocean plotting sheets are nautical charts designed for use at specific latitudes. They are used for ocean navigation where features such as shorelines, water depths and local tidal information are of no importance. Plotting sheets are particularly useful for plotting … Continue reading

## Short Distance Sailing And Rhumb Line Sailing

In my previous post about the meridian passage long method, I demonstrated how the ‘Short Distance Sailing Formulas’ are used to calculate a vessel’s position at meridian passage.  I have since received several questions asking how these formulas allow for … Continue reading

## Survival – Finding Direction From The Moon.

Just as the Sun can help us to find our general bearings during the day, so can the Moon at night. Moonrise and Moonset.  As in the case of the Sun, the Moon will rise between north east and south … Continue reading

## How To Locate The Pole Star (Polaris)

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

## Astro Navigation – What is it and why do we need it?

Astro-navigation (or celestial navigation as it is also known) is a fascinating subject that encompasses many areas of knowledge including geography, astronomy, history and mathematics.  As you unravel the principles and techniques upon which navigation is based, you will be … Continue reading

## Latitude from Polaris

Using The Pole Star (Polaris)  To Find Your Latitude Assume that the Pole Star (Polaris)is exactly in line with the Earth’s axis produced, as shown in the following diagram. To an observer O on the Equator (lat. 0o) the Pole … Continue reading

## Spherical Trigonometry Introduction

In the diagram above, the inner circle represents the Earth and the outer circle represents the celestial sphere.  Point N represents the North Pole, B represents an observer’s position on the surface of the Earth, and U represents the geographical … Continue reading

## Distance to the Horizon

The Pharos Lighthouse.  The Pharos Lighthouse or the Lighthouse of Alexandria as it was also known, was commissioned by Ptolemy Soter the ruler of Egypt and completed during the reign of his son Ptolemy II in about 270BC.  It was … Continue reading

## Revise Pythagoras’ Theorem

If after reading some of my other posts, you feel you are a bit rusty on Pythagoras’ Theorem, here is a quick brush up for you.  We can see in the diagram below that, in the triangle ABC, if a … Continue reading