October 20, 2020

Sunrise and sunset

Calculating times of sunrise and sunset. The times of the visible rising and setting of the sun are contained in the daily pages of the nautical almanac. They are tabulated for the middle day of the three on that page and provide the Local Mean Time (LMT) of the rising/setting […]
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October 20, 2020

Twilight

Explanation of twilight. Twilight is the period of approximately one hour’s duration before the sun rises in the morning and the period of approximately one hour’s duration after the sun sets in the evening, ie between the times when the sun is 12° below the horizon and sunrise in the […]
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October 20, 2020

The marine sextant

Introduction. The marine sextant is a precision built optical instrument f which is used to measure altitudes and angles. It used to be an essential part of a ship’s navigation equipment. The sextant got its name from the fact that the length of its graduated arc is approximately one sixth […]
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October 20, 2020

Uses of the sextant

Although the marine sextant is seldom used these days due to the introduction of satellite navigation systems (ie GPS), it still can be used for the following: Measuring the altitude of the stars, sun, moon and planets in order to determine geographical position out of sight of land (ocean navigation). […]
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