How to Use Sextant at Night
The sextant is a navigational tool used to determine location. The device uses the position of celestial bodies to help you find latitude. The instrument is wedge-shaped and is based on an angle equivalent to 1/6 of a circle, or 60 degrees. It has one telescope arm that you line up with a celestial body, such as the North Star, and another to line up with the horizon. After some calculating, you can use the sextant to determine your position at night.
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Instructions
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Determine the index error before using the sextant. Line up the horizon with the mirror and look at the measurement on the arc. Record the measurement. Add it to the final calculation if it is less than 0 degrees and subtract the number if more than 0 degrees.
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2
Align the arm with the horizon mirror up to the horizon for a point of reference. Locate the North Star or moon and line up the sextant's telescope arm with the position of the star or moon.
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Center the horizon through the telescope and then move the arm along the arc until the moon or North Star appears, just above the horizon. Record the degrees on the arc to find the angle between the horizon and the celestial body.
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Record the time, down to the second. Write down in order of second, minute and hour.
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Adjust your measurement based on the index reading you recorded.
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Make adjustment for measurement of dip, refraction, parallax and semi-diameter. Calculate dip by finding the square root of the height of the eye in meters above sea level multiplied by 3.28. Then multiply the square root by 0.98. Determine refraction, parallax and semi-diameter using the almanac.
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Subtract the corrected number, or altitude, from 90 to determine location.
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Tips & Warnings
Accurately record the time. An error of 4 seconds will equal an error of one nautical mile.
References
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