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RE : http://fer3.com/arc/m2.aspx/Nitpicking-Moon-Height-Corrections-FrankReed-may-2013-g24194

Frank,

Thanks for your replies.

You wrote :
QUOTE
"It may be worth mentioning that the instructions in the NA also note that there is a small correction for oblateness which is necessarily ignored in the calculation of the Moon's standard correction tables. In the section in the Nautical Almanac Explanation with "methods and formulae for direct computation", there is actually a little procedure outlined for calculating those extra couple of tenths of a minute of arc for the Moon's altitude correction. This is hardly a practical concern, but it's nice that they included it. I've never bothered with that correction or the calculation included in the NA, but it's a nice, short formula. How close is it? How do you results compare with that nice, short formula?"
UNQUOTE

Thank you very much for mentioning this information I had been totally unaware of. Certainly it must be quite instructive to take a closer look at such little correction procedure. However, and in spite of careful research into the Copies I have at hand, namely:
- US paper editions 1982 and 1983 (EXPLANATION, Section pages 254-261), and
- PORTUGAL .pdf 2013 edition (INSTRUÇÕES PARA USO DO ALMANAQUE NÁUTICO, pages 257-270),
nowhere have I been able to locate such nice and nifty procedure, whilst you have made my mouth thirsty here. And I bet that when I have implemented it, results will be extremely close to the 3D space computation ones I have published.

Would you then be so kind (yourself or any other NavList Member) as to send me a copy (if scanned document: .pdf format preferred) of such little procedure ? Thank you very much in advance.

*******

You wrote:
QUOTE
The fact that the plumb line does not pass through the Earth's center has no real significance. The coordinates account for this.
UNQUOTE

I simply wished to observe here that, on an "ideal" ellipsoid - which is our computation support, right ? - when you are located at positions from where the local vertical lines cross the Ellipsoid Center, then the 3D space computations vanish into 2D space computations since they can entirely be carried out to their full achievable accuracy in the plan defined by the local vertical line and the Body center since such particular plan now also contains the Ellipsoid Center. Hence all 3D Space general computations results are strictly identical to the 2D Computation results as described in the file attached to " http://fer3.com/arc/m2.aspx/ACCURATE-PARALLAX-COMPUTATION-Couëtte-feb-2011-g15696 ".
This can be easily crosschecked for all points belonging to the Ellipsoid Equator, as well as to its both Poles, as long as we apply the right distance from Surface to Center in our calculations.
Accordingly the viewpoint indicated here-above is just another way - as good as any other one I would think, right ? - to help easily visualizing the fact that "The coordinates account for this" as you rightly said, and there is no reason to attempt defeating it.

*******

You also concluded:
QUOTE
PS: I notice in your account of your calculation you have included info on the value of "delta-T" saying "with TT-UT = +55.7s". I reiterate that this is obfuscation. It is ABSURD to add this information.
UNQUOTE

We have all agreed for long that for our current and Classical Celnav purposes, "delta-T" values need only to be known to +/- 6 seconds of time (or so).
Nonetheless the interest of my unchanged habit to publish my retained "delta-T" values with more digits keeps being appreciated by some knowledgeable and quite Nice NavList Colleagues who are in positions to understand and experience all its benefits. It comes very handy (and in particular for the Moon as a fast moving body) if one is to make accurate comparisons on computed coordinates especially when referring to various Data sources. A few of these Nice Colleagues (at least 2 "Heavy Weights" as regards computation accuracy) have openly indicated here in the past that they concur with this continuing way of presenting information.

Thank you for your Kind Attention, and

Best Regards

Kermit
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