Celestial navigation explained - page 3


Celestial mechanics - a blueprint


The reference is now the horizontal coordinate system.

When we observe a star from our local horizon, we can define its position in the sky by its Azimuth (0° to 360°) and its altitude h (0° to 90°).

The zenith distance z is 90° minus h.

In practice, we are only measuring the altitude h of the star, its azimuth is calculated.

horizontal coordinates  
 
If you recall, we have already seen that our circle of position is centred on (delta, GHA) with a radius z.

Thanks to the Nautical Almanac, we can define the position of the star S on the celestial sphere (declination delta, Greenwich Hour Angle GHA).

From our our local observation of the star, we can measure its altitude and deduce its zenith distance z.

equatorial and horizontal coord.

We just need to find a mathematical relation between what we know (delta, GHA, h) and what we are looking for (latitude, longitude Gw ) and that will solve the problem of the celestial navigation! 

 

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