Tuesday, October 30, 2007


Finding the of GHA and declination of the SUN which is done by using the following problem as an example:

Problem 1:
On the 26 February, 1981, your vessel's 1615ZT DR position is LAT 25-14.0S LONG 57-22.0'W, you take a celestial sight of the sun. The chronometer time of the sight is 8h 13m 19s. The chronometer error is 01m 46s slow. Compute the GHA, Dec., and LHA

DATE 26 February 1981
DR LAT 25-14.0S
DR LONG 57-22.0W
ZT 26th 1615
ZD +4
GMT 26th 2015
CT 8h 13m 19s
CE + 01m 46s slow
CCT 26th 20h 15m 05s
GHA 116-47.0'
M&S 3-46.3'
SHA - - - - - - - - --
V -- - ~ - - - - - -
GHA (SUN) 120-33.3'
DR/LONG - 57- 22.0'W
LHA 63 - 11.3'
TAB DEC S 8-31.0'
d corr (0.9) +/- 0.2
DEC S 8030.8'

Using GMT, and Greenwich date of observation, enter the Nautical Almanac and record tabulated hourly value of GHA and TAB DEC. in your format
At the foot of each declination sub-column, which applies to the sun, a number is found which is used for interpolation for any left ­over minutes of GMT. This number is called the "d", in this case "d 0.9" This is the average over the three day period that the declination changes per hour of GMT. The "d" is recorded on the D CORR line off to the side. This is a correction, as with any correction, it is either a + or - . If the declination increasing (getting larger), then it is a plus ( + ) correction, if the declination is decreasing, then it is a minus ( - ) correction.
Step 3
Turn to the yellow pages of the Nautical Almanac, and find the "15 minute page," enter with "5-seconds." Then under the Sun and Planets column find the increase in the sun's GHA since the last tabulated (hourly) value, hence 3° 46.3' is your M&S correction and enter this in your format. Always add the GHA and "m & s "tabulated value together to get the total GHA
Step 4
While on the 15-minute page under the "v" or "d" correctioncotumn, find the "d" 0.9 on the left hand side. This is equal to 0.2', enter this in your format and in this case subtract. This will be, the declination (dec) of the sun aUhe time of sight.
Step 5
Bring down your DR longitude and enter it in your form. The rule is:
LHA = GHA + EAST LONGITUDE ,LHA = GHA - WEST LONGITUDE So, we subtract our DR longitude to get the 'LHA