Taking a real life sextant sight can take anywhere from 30 seconds to 15 minutes...depending on the weather (wx). Under bad conditions, it's impossible.
What the navigator is trying to do is simultaneously view the horizon and the heavenly body. The celestial body is reflected into his field of view by two small mirrors while he adjusts the micrometer drum (the dial at the bottom of the index arm), precisely when it appears as if the body is resting on the horizon, he yells, "MARK", loudly if very windy. His assistant/time-keeper, annotates the time in the navlog by Hour:Minute:Second. The Nav then calls out the Angle of Elevation (read from the Arc at the bottom of the sextant), to the assistant, who jots that info into the log as well. After gathering enough sights, (Five or more for the Sun for an average), they head below or out of the wx to begin their sight-reduction.
Two things needed for Sight-Reduction:
Current Almanac and Sight-Reductions Tables. In RL that could be HO Pub 229, HO Pub 249, or HO Pub 211. Or, if mathematics is your game, by the following two formulae:
Hc = asin [(sin Lat sin Dec) + (cos Lat cos Dec cos LHA)]
Z = acos [( sin Dec - sin Lat sin Hc) / (cos Lat cos Hc)]
What is needed to make your sight in the game:
1) Select a body, pause Stellarium program, jot down the HH:MM:SS and it's Altitude.
2) Resume Stellarium, Select another body, pause Stellarium, jot down theHH:MM:SS and it's Altitude.
3) Resume Stellarium, Select another body, pause Stellarium, jot down theHH:MM:SS and it's Altitude.
4) Exit Stellarium,
From Almanac:
Get:
Sidereal Hour Angle (SHA) of Aries and Declination (Dec) if using Stars,
Greenwich Hour Angle (GHA) of Sun, Moon, & Planets.
Minute/Second Increments
Add them up by xxx° xx.x'
Add East Longitude (Assumed Long)
Subtract West Longitude (Assumed Long)
Answer = Local Hour Angle (LHA)
Use Angle of Elevation from Stellarium as the "Ho" (Observed Height)
(In RL several corrections are needed to discern the true Ho) We won't need to make corrections when using Stellarium.
From the Sight-Reduction Tables:
Get by Assumed Lat, LHA and Dec:
Hc d Z
Hc = the scientifically calculated Altitude of the body.
d = declination correction.
Z = Azimuth of the body.
If Ho > Hc, then subtract Hc. The difference is the distance in nautical miles your line of position (LOP) is in the direction
toward the observed body
If Hc > Ho, then subtract Ho. The difference is the distance in nautical miles your line of position (LOP) is in the direction
away from the observed body.
From an Assumed Position (usually an intersection of the Assumed closest Lat/Long) construct a intercept line the length in Nautical Miles toward or away from your Zn of the body. At the end of this intercept line, construct a perpendicular line which will represent your LOP.
Continue this process until all your celestial bodies are done this way. When finished, all your LOP will cross in one position or pretty close to one spot. This spot is your Sight-Reduced position.
In theory that's how it's supposed to work. Your results may vary....
