NavList:

> I got 1907 for NT, but I’m not going to quibble.  What is wrong is
> that this is the Time in LAT

I'm not sure what "LAT" is, but the times in the NA are UT/Z unless I
don't remember correctly (?).

> What is wrong is that this is the Time in LAT which must be
> converted to ZT before use. 

Again, not knowing what "LAT" is I can't discuss this one way or
another, but as I understand it all of the times on the NA page
(sunrise/sunset/twilights/meridian passage/GHA/etc.) are all in UT/Z.

> These times are only good on the Zone reference meridians, including
> Greenwich (divisible evenly by 15).

Correct, and the arc-to-time conversion changes that time to the UT/Z
time at the given DR longitude position. Applying the ZD correction
brings the time back to local zone time (for the convenience of the
navigator, but not used in the LHA Aries calculation).

> Here is where we get really different.  The correction from LAT
> to ZT should be fairly small (<1 hr) if we are keeping the correct
> zone description.

Aha - I think the difference here is from the different way we we
(apparently) calculate local times for suneset/twilights.

> The trouble with the second is that you have to apply the correction
> in the correct direction which can be confusing, especially if you
> are in East Longitude and are from the Western Hemisphere.

Correct - and since events happen earlier in eastern longitudes you'd
subtract the (absolute value of) the ZD from the UT/Z time given in the
NA to change the time to the local time zone.

> I got 146 degrees since we add 22’ longitude to 34.7’ GHA to get 56.7

> which is close to 60, and we carry the one to 145 to equal 146.

I'll have to look at my worksheet tomorrow to see how I arrived at that
LHA, but I'm reasonably sure that I remembered to add 1 whole degree to
it.

> I also use Pub 249 Vol 1 but Epoch 2010 (available online).

Aha, wasn't aware that 2010 was out yet (though it might not be in
printed form yet) - thanks for the info.

> Obviously since my LHA is different from yours, there will be
> slightly different results:

Agreed.

>> correction for precession and nutation
> This is correct, but not necessary for precalculation as we
> only need an approximate Hs and Zn to find the body.

Ah, seems like you mentioned getting Hc and Zn - thought you'd meant to
get values for the final sight reduction, but you're correct that an
approximate Hs/Zn will work to get the body into the sextant's field of
view.

> Also, I was taught to only apply this correction in off-epoch years
> to the actual fix instead of the LOP’s (unless there is just one LOP
> of course).

According to the instructions in my copy of Pub. 249, the correction
can be applied to either the LOP or the fix itself (and personally I'd
rather move just the final fix than the several LOPs used to determine
it) - less time, and less prone to errors.

> The point of pre-calculating stars at sea is so that you can go out
> and just point the sextant in the correct Azimuth, then the star just
> pops into view.  A tiny adjustment on the micrometer drum and you
> take your sight. 

I've tried to do that from my front/back yard in recent weeks (using an
approximate eye-level on the neighbor's houses) but so far I've only
been able to make it work for a couple of the selected stars (there
isn't much light pollution where I live, but it's still not the same as
being out on the open water away from civilization).

> I can shoot a round of stars in under 10 minutes, and am just usually

> waiting for the dimmer ones to appear.  For this round, I
> shot 5 bodies in just over 7 minutes.

How many shots of each star do you usually take? I've heard conflicting
philosophies on this - one says to take ~3 of each star, the other says
just to take one of all of them (assuming they're all in view) and any
errors will be obvious when the resulting LOP doesn't land reasonably
close to where the others cross.