Noon for any celestial body (Sun, Moon, Planet or Star) is the time when it crosses an observer's meridian. This means the body will be directly north, south or right overhead. By measuring the body's angle above the horizon with a sextant the angular distance along the earth's surface can be calculated. If the body's Declination (Celestial Latitude) is know then the observer can calculate their Latitude. To measure a celestial body's altitude by means of a sextant the observer must be able to see both the body and the sea horizon. A sextant is used to measure the angle of a celestial body above the sea horizon.
Note: Longitude cannot be determined by this method because the celestial body's altitude changes so slowly at its noon that the actual time of noon cannot be accurately measured.
Example:
1 - If a celestial body is right overhead then its 'True Altitude' will be 90º and its 'True Zenith Distance' will be 0º. The observer will therefore be at the body's Declination, which can be found in astronomical tables.
2 - If the 'True Altitude' of the sun is 64º South of the observer at noon then the observer is 26º North of the sun. If the sun's Declination is 15ºS then the observer is 11ºNorth of the Equator.
Noon for any celestial body (Sun, Moon, Planet or Star) is the time when it crosses an observer's meridian. This means the body will be directly north, south or right overhead. By measuring the body's angle above the horizon with a sextant the angular distance along the earth's surface can be calculated. If the body's Declination (Celestial Latitude) is know then the observer can calculate their Latitude. To measure a celestial body's altitude by means of a sextant the observer must be able to see both the body and the sea horizon. A sextant is used to measure the angle of a celestial body above the sea horizon.
Note: Longitude cannot be determined by this method because the celestial body's altitude changes so slowly at its noon that the actual time of noon cannot be accurately measured.
Example:
1 - If a celestial body is right overhead then its 'True Altitude' will be 90º and its 'True Zenith Distance' will be 0º. The observer will therefore be at the body's Declination, which can be found in astronomical tables.
2 - If the 'True Altitude' of the sun is 64º South of the observer at noon then the observer is 26º North of the sun. If the sun's Declination is 15ºS then the observer is 11ºNorth of the Equator.