v for the sun

[c_davidson]

hi,
why there's not v correction for the sun GHA?
In italy the "Nautical Almanac" have the v correction for the sun.
Maybe its not important but sometimes give me a correction of 0.2'/0.3' on the sun GHA

thank you!
Alberto

Alberto,

The Nautical Almanac, either on this site or from the USNO doesn't list a v correction for the Sun.  Given the accuracy of a position determined using a sextant isn't exact or precise a difference in position by 1 nm is no great amount.

If you'd like to, it's easy enough to obtain the v correction by comparing the Sun's GHA of the time of the sight to the next hour's GHA of the Sun.  For example, today, March 30, 2017, the Sun's GHA is increasing per hour by 15° 00.2'    The v figure is positive and is increasing about 0° 0.2' minutes per hour.  For this date only, that's not very much of an increase in GHA or a correction that is necessary to get a good LOP.  It would be more precise to correct for the Sun's GHA v figure but that takes more time and would probably be considered unnecessary. 

That's also why we don't correct for the Sun's "d".  It won't make that much difference in your position and your pencil width, even with a pencil of 0.5 mm, when drawing the LOP will often render even the most accurate figures to be incorrect (though not by an amount that one should be worried about).

Clen