Competence 1: Plan and conduct a passage KUP 1: Ability to use celestial bodies

KUP 1: Ability to use celestial bodies

sheng 2 Courses

Learning objective:

Celestial navigation is an important navigation method to determine the precise location of a vessel or aircraft, primarily using the positions of celestial bodies (such as the sun, moon, and stars). The learning objective is to acquire the knowledge:

Principles of Celestial Navigation: Celestial navigation involves using the altitude and azimuth of celestial bodies to calculate ship´s position on Earth.
Calculation Methods: These can be divided into tabular methods and computational methods. Tabular methods involve looking up celestial body positions in resources such as the Nautical Almanac, while computational methods rely on mathematical formulas and computers for precise calculations. (Almanac: a book published every year that tells you about the movements of the planets, the times of the tides , and the dates of important events)
Height Difference Method: This is a common measurement technique that involves measuring the altitude of the same celestial body at different times to determine the vessel’s position. This method requires precise instruments and corrections for altitude calculations .
Position Error: Position errors are crucial factors to consider in celestial navigation. These involve corrections for observational accuracy and calculation errors.

Learning content:

1. The process of Celestial positioning:

Observation: Using a sextant, the navigator measures the angle (altitude) between a celestial body and the visible horizon. The sextant allows for precise measurement of this angle, which is crucial for accurate positioning.
Recording Time: The exact time of the observation is recorded using a chronometer. Accurate timekeeping is essential because the position of celestial bodies changes continuously as the Earth rotates.
Calculating Position Lines: The measured altitude and the recorded time are used to calculate a position line, a line on the Earth’s surface where the observed celestial body would appear at the measured altitude. This calculation involves using nautical almanacs, which provide the positions of celestial bodies at any given time, and sight reduction tables, which help convert the observations into useful navigational information.
Intersection of Position Lines: By taking observations of multiple celestial bodies, a navigator can plot multiple position lines on a chart. The intersection of these lines provides the ship’s precise location.

2. The sextant

The sextant used in the celestial positioning is a doubly reflecting navigation instrument that measures the angular distance between two visible objects. The primary use of a sextant is to measure the angle between an astronomical object and the horizon for the purposes of celestial navigation ¹.