nautic_almanac Files

This program is intended to solve the calculation of the altitude of a given body and determine the position of the observer on the earth.
It also corrects the sextant's errors as per HO Nautical Almanacc method.

Date and Estimate Position:
Required date and estimate position should be inserted in the edit boxes on the main window, default date is the actual date.

Time:
The time section shows the UTC time by clicking the Start button, the stop button stops the chronometer, the local time
edit boxes show the local time for a given UTC time from the actual longitude pressing the button 'Local'.
Inserting a Local time the "Local time: " edit boxes UTC time will be shown on the "Time UTC" section pressing the button 'UTC'
this is useful for example to get the UTC time of the meridian passage of the sun (plus or minus 15' from 1200 at the maximum altitude).
Local time is meant to be the time at the actual meridian and is not to be confused with the zone time, to get the zone time for a given longitude just add or subtract the fuse value (1 hour every 15° add toward Est and subtract toward West, for a better evaluation of the legal time check the zones time map).
If the time to consider is that of your actual position, the zone time is that shown by your watch.

Observation:
On the left side of the window, in this section, the uppermost combo box shows a list of celestial bodies, once selected and pressed the button "Calc Altitude", the calculate altitude will be shown in the box "Calculated alt:" computed by a series of algorithm developed by SOFA (Standard of Fundamental Astronomy http://www.iausofa.org/current_C.html) also used for the calculation of the Hydro-graphic Office Nautical Almanac.
The combo box below "Solar System:" selects the planets the sun and the moon, pressing the button "Calc Altitude" works in the same way as above.
Once performed one of the above actions in the box "Azimuth:" we can read the true bearing of the body, this is very useful to correct the compass error on board of vessels.
Pressing the button "info" shows a window displaying a series of ephemeris data referred to the body selected.
In the three edit boxes beside the label "Observed Altitude"  the degree, minutes and second taken from the sextant reading should be manually inserted, in the "Index error" box and in the "Eye height" box should be inserted the instrument index error and the height above the sea level of the observer's eye accordingly.
The "upper limb" check box is to be selected in case of observation of the upper limb of the sun or the moon.
Exiting the "Eye height" box, after the value insertion, and  clicking elsewhere , on the box "Intercept:" will be shown the difference in nautical miles from the true position line observed and that calculated using the estimated position.
This position line is perpendicular to the bearing of the body, the crossing of at least two of these lines determines a true position on the earth's globe.(A position obtained with astronomic observation is considered good  if its range of error doesn't exceed a couple of miles). The true altitude corrected for instrument and refraction errors will be shown on the box named "True Altitude".
The button "Save", saves each body data in order to be shown later on the plotting sheet. (at least two bodies must be observed)
The button "Cancel Saved" on the following section on the bottom left side of the window cancel the bodies data previously stored.

Getting the name of an unknown star:
Observing the altitude of a body and inserting it in the edit boxes as explained above together with its bearing on the "Azimuth" box, the name of the body will be shown on the box "Star unknown". 

Position:
There are three buttons: the button "Cancel Saved:" as already explained,
the button "Meridian" calculates the value of latitude when the body's azimuth is very close to 180°, this is usually made by the sun passage at noon.
the button "Calc Position" opens a Plotting Plan showing a Cartesian diagram whose centre is our Estimated position , the north on top, and the intercept drawn perpendicularly to the bearing together with its direction shown by the two small arrows at the edge.
With at least two intercept drawn, their intersection gives the position witch is reported on the bottom left side of the Plotting plan and also in the "Latitude:" and "Longitude:" boxes in the main window.

Pressing the "Sky view" button a view of the actual sky at 360° range will be showed and the background may be dragged to change the point of view of the observer, the azimuth is displayed on the bottom of the window as a compass rose, and the altitude of the celestial bodies will be shown at each cardinal point. The moon will show its actual phase and the sky will change background according to the enlightening of the sun. This will be useful for the recognition of the first determination of the position of the celestial bodies.

The same operations may be performed by the aid of the menus under the status bar.

Version: 1.6-4   24 August 2021
Copyright (C) 2011 Giovanni Enas
License: GPLv3