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StarPilot Sight Reduction function

If no special options are taken, sight reduction proceeds in a step-by-step sequence. Select Sight Reduction from the main menu, then select the body.

StarPilot then asks for the sight time, and date, body name, DR Lat and Lon, as well as the Index Correction and Height of Eye. In this example we will be doing 3 star sights — the example from the 1999 Nautical Almanac. They all have the same DR position, date, IC, and HE, so we are better off storing these values so we don't have to enter them each time.

Going back to Settings, we proceed to enter the values used in this example: date = July 4, 1999, DR = 32° 00' N, 15° 00' W, with HE = 0 feet and IC = 0.0 See notes in the USNO example on how these specific values ended up here.

Now enter the IC and HE...

And finally, set Sight Reduction Mode = Sequential, so StarPilot knows to use the stored values and not ask for new ones on each sight.
Now entering the 3 star sights is just a matter of entering the sight time, star name and sextant altitude (Hs). On the last sight, we show what to do if you do not know the star's number.

The first is a Regulus (star# 26) sight at 20h 39m 23s GMT with Hs = 27° 15.90'
The next is Antares (star #42) sight at 20h 45m 47s GMT with Hs = 25° 59.22'.

(Note that the sample sights given in the almanac are presented to the precision shown, but real sights clearly cannot be that accurate. Sextant sights are only accurate to about 0.1' at best.)


The answer is a = 2.2' Away from 267.3°. Intercepts (a-values) that are negative are "Away," positive ones are "Toward." Note that the full list of input data is shown in the output so we can make a quick double check that that input was correct if the output seems strange. Note also the simple input format for angles and times.

The third sight is Kochab, at 21h 10m 34s with Hs = 47° 28.88', and we will assume we do not know its star number.

In this case select "O" for a list which will then display the submenu along the bottom of the screen. Since "K" for Kochab is between F and M, we press the F3 key to go straight to that part of the list. Note the star number is 40, then press [Exit] to get back to the sight reduction screen, enter 40 and proceed. All 173 stars are listed. The number to the right (2.2 for Kochab) is the brightness magnitude of the star.



That completes the examples of sight reduction. The procedure is identical for other bodies.

You can review the stored sights with the Review sights option. These examples are discussed in the Fix by USNO and Fix by Plotting examples.

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