Checking a Compass by the Sun

The OP asked a general question in his heading about observations of the sun.
In his post referred to amplitudes.

For a general observation of the compass error, at a time other than sunset or sunrise you can get a reasonably accurate observation of a low altitude star, planet or moon using a hockey puck style hand bearing compass with no concern about you eyesight.

The moon is bit of a pain due to more corrections planets require identification but due to movement are more difficult to identify than stars.
So use a Bright star some where between about 20 and 30 degrees above horizon.
Identify with star chart and or from constellations.

If you have a shadow pin or shades the sun works very well.

Pick your bright star.
Make note of time GMT as accurately as possible.
Make Note of DR position lat and long or use GPS.
Make not of azimuth or bearing of star.
Make note of heading by hand compass.
Make note of heading by steering compass.

(It’s a lot easier with two people taking simultaneous observation of headings)

To calculate. By calculator.

Look up in almanac for day and hour.
The GHA of Aries..
The Increments for minutes and seconds.
The SHA and Declination of your bright star
Apply longitude. Ad east subtract west.
This will give you the LHA of the star.

You will need to calculate you A,B and C corrections. Or you can look up A and B corrections in nautical tables.


A Correction = Tan Latitude/Tan LHA

B Correction= Tan Declination/Sine LHA

If Latitude and Declination are the same.

C Correction = A+B

If Latitude and declination are different

C Correction = A- B

CoTan Azimuth = C Correction Cos Lat

Azimuth = 90- Anti Tan(C Correction x Cos Lat)
 
I was watching kids tv with my 4yr old son the other day (like you do) and they suggested the watch method, may be of use, may be not?

wcompass-s.png

In the southern hemisphere, hold the watch horizontal and point the twelve o'clock mark in the direction of the sun. Bisect the angle between the hour hand and the twelve o'clock mark to get the north-south line. Before noon, north will be the direction closer to the sun; after noon, it will be the further direction.

Gareth
 
It is remarkable what degree of accuracy and reliability can be obtained using a sextant.
But for ease, I always used the amplitude tables in the front of Inmans, taking the bearing as the sun "sat on" the horizon. This was normally a good working allowance for refraction.
Given normal steering errors, strict accuracy is unecessary in a steam ship
During the day, I used the alt/az tables HO 213, which gave accuracy as good as one's sextant technique.
My best sight ever (go on let me tell you, I am so proud of it) was from a few miles south of the Comoro islands. On a quiet Sunday afternoon about 1500, when most of the ship wa s asleep, I took nine obs each of the sun the moon and venus and the nine horizontal sextant angles of four points on the island.. Sent to droggy, the islands were moved 1.25 miles to the south-east.
To take very accurate sights: work out in advance what the approx elevation will be, get someone else to hold the watch. You "shoot" as th esun comes on, move the wheel 3 units, shoot again and so on for at leasst six shots.
Tabulate the times, and take first differences. Because all the elevation diffs will be the same, any duff sights will stick out. Average those with a reliable dif either side and note it.
This method virtually eliminates error.
I have over 4,000 sunsights in my work book and I have no centre to the retina of my right eye.
No regrets.
 
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