A Sea Vagabond's World by Bernard Moitessier

Author:Bernard Moitessier
Language: eng
Format: epub
ISBN: 9781493042814
Publisher: Sheridan House

Sun altitude and meridian

When the sun reaches its greatest height for the day (at true noon), we say that it “passes the meridian.” The angle formed between the observer’s eye and the horizon is the “meridian altitude.” So what we call the “sun’s altitude” actually refers to the angle formed by the intersection of two lines: a horizontal one, between the eye and the horizon, and another one, from the eye to the sun. This “altitude” (which is actually an angle) is called “meridian altitude” when it is measured (with a sextant) at the exact instant when the sun is at the highest point in its arc that day, at true noon.

The sun’s meridian altitude reaches 90 degrees (that is, with the sun directly overhead) twice a year for every point on earth located in the tropics (between 23° 27' north and 23° 27' south), but is always less than 90 degrees outside the tropics. At the Arctic and Antarctic circles, which are located at 66° 33' latitude north and south, respectively, the sun’s meridian altitude is never greater than 23° 27', and it reaches that altitude only once a year.

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