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Stan,

There is no v correction for Sun in the Almanac.
And they explain on p. 255, 4.
"v is zero for Aries and negligible for Sun".

Thus the Sun GHA at x hours 0 minutes 0 seconds is exactly what
the daily page of the almanac says.

There is no d correction for Aries. Aries declination is always 0.
There is d correction for Sun, but it is small, usually less that 1.0.
If you look for the correction for d=1.0 at the Corrections tables
for 0 minutes, you see that the correction is 0.

Thus the data on daily page for x hour 0 minutes 0 seconds is exact,
(or has negiligible error for Sun) and the use of Correction table
is not needed for this case.

The explanation in the Almanac is complete but very brief, indeed, I
agree.

Alex.

On Wed, 4 Apr 2012, Stan K wrote:

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> Gary,
>
> Yes, it seems like nobody ever noticed that situation!
>
> I understand all this, but it doesn't help.
The problem is not with the mathematics but with the
proper procedure when doing an "on paper" sight reduction,
i.e. with a typical sight reduction form.
It still seems that if you follow the instructions in the Almanac,
for the 0 minutes case we are discussing,
any time the v or d value is between 6.0' and 17.9',
for example, you would be adding a v or d correction
of 0.1' to the hour value on the daily page, which appears incorrect.

> And when would the v and d data of the 0 minutes column ever be used?  When 
there are 0 minutes but non-zero seconds?  Not according to the Almanac 
instructions.
>
> I've looked for an e-mail address for someone at the UK Hydrographic Office.  Know of any?
>
> Stan
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>
> -----Original Message-----
> From: Gary LaPook 
> To: NavList 
> Sent: Wed, Apr 4, 2012 12:46 pm
> Subject: [NavList] Re: A basic sight reduction question
>
>
>
>
> I never noticed the  situation that you pointed out. The answer is that the 
"v" and "d" correction tables in the N.A. are simply multiplication tables, 
multiplying the "v" and "d" factors (which are simply how much the body 
changes its position in one hour) by the proportion it will change in a 
period less than a full hour. Since the tables only list correction for whole 
minutes they are actually the average correction for the whole minute 
tabulation so they are actually calculated for m + 30 seconds. They can be 
considered precise only for the +30 sec case and approximate for other times. 
If you wanted more precision then just divide the "v" or "d" by 3600 and 
multiply by the number of seconds after "on the hour." If you do it this way 
then you will find the correction for "on the hour" is zero, zero seconds 
times any "v" or "d" value will always equal zero. But you are trying to make 
it too hard on yourself.
>
> gl
> --- On Wed, 4/4/12, slk1000---com  wrote:
>
>
> From: slk1000---com 
> Subject: [NavList] A basic sight reduction question
> To: navlist---org
> Cc: slk1000---com
> Date: Wednesday, April 4, 2012, 6:50 AM
>
>
>
> I have always though that the hour values of GHA and Dec on the daily pages 
of the Nautical Almanac were "exact" (on page 255 of the Nautical Almanac:  
"The daily pages give the GHA and Dec...for each hour of UT."), and that 
everything else (minute/second GHA increment and v and d values and 
corrections) concerned adjustments for sights not being taken on the hour.  
Now I am not so sure.
>
> For the first time, I have had to concern myself with sights taken on the 
whole hour (minutes and seconds are zero), and I am not clear as to how they 
should be handled.  Based on my original thinking, just use the hour value of 
GHA/Dec, and nothing more.  But according to page 256 of the Nautical 
Almanac:   "The table of Increments and Correction for the minute of UT is 
then selected.  For the GHA, the increment for minutes and seconds is taken 
from the appropriate column opposite the seconds of UT; the v-correction is 
taken from the second part of the same table opposite the value of v as given 
on the daily pages."  So if the minutes value is zero, you go into the 0 
minute block (the "same table") with the value of v from the daily pages and 
extract the value of the v correction, no?  (This all applies to Dec also.)
>
> If this is wrong, then why show v/d values and corrections for 0 minutes at 
all?  Where would they be used?
>
> And then what if the minutes are zero but the seconds are not?  Is that another "special case"?
>
> Practically speaking, this is no big deal, since the v/d correction is 
either 0.0', 0.1', or 0.2' (and that only for a v/d value of 18.0') for 0 
minutes, but using the corrections for whole hours is either right or wrong.  
I cannot find any examples showing this situation.
>
> Am I way off base here, or does the explanation in the Almanac leave something to be desired?
>
> Hard to believe that for all the time I have been doing CN, this is the 
first time I have asked myself these questions.
>
> Stan
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> : http://fer3.com/arc/m2.aspx?i=118693
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