Using the exact time of observation, the nautical almanac, spherical trigonometry formulas and dead reckoning, we can determine the calculated sextant altitude of the sun.
That is to say, the calculated altitude of the sun of our dead reckoning position
In summary, the goal is to calculate the observer’s altitude using the Dead Reckoning (D.R.) position and the observed altitude of the sun using the sextant.
These two altitudes need to be compared and serve as the basis of the Marcq St. Hilaire method.
Keep in mind that the entire context of this website begins with the La Rochelle exercise, guiding you to an interactive worksheet. The singular objective is to learn how to determine your line of position at sea through eight identical exercises.
theory Hc (the calculated altitude)
In fact, the formulas of spherical trigonometry enable us to calculate measurements from the center of the Earth to the center of celestial bodies, including the Sun, stars, planets, and the Moon.
Calculated sextant altitude and dead reckoning:
The formula:
L = Latitude of our dead reckoning position.
P = Polar angle
After reading through this page, you can proceed to another section where you’ll find two examples illustrating how to calculate the “calculated altitude (Hc)”.
Next, we calculate the azimuth of the sun :
Next, we calculate the azimuth of the sun using almost the same inputs and the calculated altitude we obtained previously.
To clarify, We always calculate Hc first, then the azimuth, since its formula requires Hc.
D = Declination of the sun.
L = Latitude of our dead reckoning position.
Hc = Calculated altitude of our dead reckoning position
What to do with the calculated altitude? See the Principles Step 4
Calculated sextant altitude(Hc) and dead reckoning:
A very interesting site is the NOAA sun calculator
Firstly, the NOAA Sun Calculator is a tool provided by the National Oceanic and Atmospheric Administration (NOAA) that allows users to obtain information about the position of the sun at any given location and time. It provides data such as sunrise, sunset, solar noon, and twilight times.
Furthermore, the calculator takes into account various factors, including the observer’s geographic location (latitude and longitude), date, and time zone.
As a result, by inputting these parameters, users can generate accurate and detailed information about the sun’s position
