A Simplified Guide to Small Marine Craft Navigation.

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Chapter 2 (v.1) - Measurement of Direction.

Submitted: December 02, 2016

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Submitted: December 02, 2016

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Measurement of Direction.

 

Everyone knows that the Sun rises approximately in the East and sets approximately in the West. Why this is so is on the illustration shown below in how sunlight falls on the Earth's surface. Navigational “Direction” is therefore related to the movement of planet Earth, which rotates once on its axis every twenty-four hours in the manner indicated by the arrow on the illustration.

As the Earth rotates the parts of the Earth experiencing darkness, the shaded section, and the parts of the Earth experiencing daylight, the white section, will change, the dividing line between the shaded and white sections representing the point at which the Sun appears to ”rise" to an observer on the Earth's surface. The dividing line between daylight and darkness on the far side of the Earth is the point at which the Sun would appear to "set” to an observer on the Earth's surface.

 

 

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Earths rotation and "direction". In the next illustration N and S represents the fixed axis about which the Earth rotates, and the points N and S are called the Earths poles. The letter E represents EAST, and is the "direction" in which any point on the Earth's surface is being carried by the rotation and is shown by the arrows. The letter W represents WEST, and is the opposite "direction" to this, 180° from East.

The letter N, represents NORTH, and is the "direction" lying 90° to the left of an observer facing east, the pole in this "direction" being referred to as the North Pole”.

The letter S represents SOUTH, and the South Pole lies 90° to the right of the same observer. The four "directions" of, North, South, East and West are the cardinal directions in navigation.

 

 

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There are many other “directions” that will have to be discussed later, but as the already mentioned angles 90° and 180° play a very large part in calculating ”direction, and numerous other aspects of navigation, budding navigators must understand how such angles are measured.


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