CELESTIAL NAVIGATION & MARKERS
Celestial Navigation, also known as Astronavigation, is a position-fixing process that has enabled sailors to cross featureless oceans with certainty and target un-sighted land with precision. Astronavigation uses angular measurements or sightings between the horizon and a common celestial object to perform navigational problem-solving. Although the Sun is the most often measured celestial object, more sophisticated navigators are prepared to use our Moon, other planets, or one of 57 "navigational stars" described in nautical almanacs to observe the positions of these celestial objects relative to the observer and a known location.
The key rule to celestial navigation is having a fixed, known reference point such as a bright star easily visible in the night sky at the time of year you're sailing.
Use of Time
One method of celestial navigation requires accurate time-keeping. So, the use of time to navigate by the stars depends on an accurate timepiece (such as a chronometer) in an attempt to assess the time of a sextant sight.
Traditionally speaking, a navigator would assess a chronometer from a sextant, at a specific geographic marker outlined by a certified astronomer. Nowadays, this skill is quite rare, as most navigators can no longer do that.
Traditionally, three chronometers were kept in gimbals in a dry room near the center of the ship. They were used to set the time for the actual sight, so that no chronometers were ever exposed to the wind and salt water on deck. Winding and comparing the chronometers was a crucial duty of the navigator. Even today, it is still logged daily in the ship's deck log and reported to the Captain before eight bells on the forenoon watch (shipboard noon). Navigators also set the ship's clocks and calendar.