The data for the following example are from John Karl's "Celestial navigation in the GPS age" (First Edition, 2007), pp. 63-65.  With three spreadsheets we reproduce the computations for the sight reduction of the Moon observation presented in Figure 6.4 on p. 64.  Given the dead-reckoning (DR) position and the recorded time of observation (UT), the Moon sextant altitude (lower-limb) is reduced to intercept distance and azimuth needed to plot the associated line of position (LOP) according to the intercept method of Marcq St. Hilaire.

Input data:
Body: Moon, lower limb
Date: 11 May 2005
UT: 02^h 19^m 14^s
Hs: 25º 21.6'
Sextant index correction: -3.3'
Height of eye: 9 feet
assuming standard atmospheric conditions
DR position: S 34º 13', E 161º 43'

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moon.xls:

Input:
Date: 11 May 2005
UT: 02^h 19^m 14^s
In cells A2-F2 entered: 2005 5 11 2 19 14

Output:
GP (row 5)
GHA: 182º 25.4' (same as 181º 85.4' in the book)
Dec: N 27º 42.9' (difference of only 0.1')

Semidiameter (SD, cell A8): 15.0'
Horizontal parallax (HP, cell C8): 55.1'

Note that there is no need for increments and corrections (v or d Corrⁿ).




This "almanac" spreadsheet for Moon is available here for a free download.

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alt_corr.xls:

Input:
Height of eye (cells E1, F1): 9 ft
Using standard conditions for temperature and pressure:
Pressure (cell E2): 1010 mb
Temperature (cells E3, F3): 10 degrees Celsius
HP (in arcminutes from moon.xls cell C8): 55.1 entered in cell E6

Sextant altitude (Hs): 25º 21.6', entered as 25 216/600 in cell B1
Index correction: -3.3', entered as - 33/600 in cell B2
Artificial horizon was not used: entered N in cell B4
SD (in degrees from moon.xls cell A8): entered (+)15/60 (positive for lower limb observations) in cell B11

Output:
Observed altitude (Ho) in cells B12-B14: 26º 18.2' (difference of only 0.1')

Note the intermediate result for apparent altitude (Ha) in cells B6-B8: 25º 15.4' (same as in the book)

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intercept.xls

Input:
Assumed position (AP) is taken to be the dead-reckoning (DR) position:
Latitude: S 34º 13', entered as -34 13/60 in cell A2
Longitude: E 161º 43', entered as (+) 161 43/60 in cell B2

GP of Moon from row 5 of moon.xls:
GHA: 182 254/600 entered in cell C2
Dec: (+) 27 429/600 entered in cell D2

Ho from alt_corr.xls cells B13, B14: 26 182/600 entered in cell E2

Intermediate results:
LHA (cells F2, F3): 344º 08.4' (same as in the book)
Computed altitude (Hc in cells A6-C6): 26º 16.4' (difference of only 0.1')

Main results:
Intercept (cells D6, E6): 1.8 Toward (difference of only 0.2')
Azimuth (cell F6): 15.7 agrees with 16 from the book after rounding

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worksheet.pdf:

The data from this example are summarized in the worksheet below; input data are marked as green, and spreadsheet results (some of which are relayed as input for subsequent calculations) are blue.