NavList:

Antoine, you wrote:
"To recap, lower and lower altitude refraction random errors do render Lunar distances more and more inaccurate .... So, why should we bother with the (subtle ?) distinction between the Great Circle joining the refracted centers and the shortest Great Circle joining refracted limbs ? Well, this still remains an interesting subject to study and play with ..."

There's a calculation of this in one of the old 19th century nautical astronomy textbooks. I can't recall exactly where right now but it's probably Chauvenet. It's an exceedingly small correction (note for anyone following along: this is NOT the correction for refractional flattening but a more subtle alignment issue). The next largest correction that we do not take into account in lunars calculations done by the standard methods is the correction for the actual shape of the Moon's limb. There are mountain ranges and impact basins along the limb that change the diameter by as much as a couple of seconds of arc. These are just below the 0.1' threshold so they can be ignored except if we're trying for that next step in accuracy. The lunar limb's outline varies with time due to the lunar librations. This is all calculable...

You wrote:
"A possible explanation for the "discrepancy" you mentioned between the NAL and AAL refraction values might come from the fact that AAL values are given for a single given CONSTANT wavelenght, while NAL gives values for the observed average wavelenghts - i.e. INCREASING WAVELENGHTS when heights decrease - since all bodies apparent colors start moving towards "red" when height decrease. This MIGHT be a resonable explanation. Any other explanations from NavList Members ?"

That's an interesting idea, but there are plenty of other possibilities. But the point you make here is important. Refraction varies with wavelength, and all common celestial objects have spectra which are nearly flat in the visible spectrum, even when they're low in the sky and reddened by scattering. There's still plenty of blue in the solar spectrum when the Sun is low. Likewise for the Moon (the lunar spectrum, of course, looks just like the solar spectrum, complete with all the absorption lines, since its light is reflected sunlight). Since refraction varies with wavelength, astronomical objects are "smeared" into little "French flags" (and yes, that's how we describe it over here, too): blue at the top, more or less white in the middle and red at the bottom. This is a physical "smearing" of the apparent position of an astronomical object, and no amount of calculation or clearing can eliminate it. That's the real problem with shooting sights at extremely low altitudes from, say, 3 to 6 degrees. The refraction tables are reliable in that range. But they apply only to one color in the objects' extended images (below 3 degrees, the refraction is variable depending on the structure of the atmospheric layers and should not be trusted to better than half a minute of arc).

And you added, regarding special signs and formatting:
"Sorry about that ... But maybe should I (we ???) harshly complain to our Forum Moderator ... ( Silence on board !, don't let him know for now !!! )
:-)))"

Ha! As soon as I can get it online, we will have a NavList-specific version of "bbcode" available. So you'll be able to add most any sort of formatting you like including professional-looking LaTeX equations. Which would you like first: threaded message views? Or nicely formatted messages with beautiful inline equations?

-FER
PS: Meanwhile, somebody please send Paul Hirose a plain vanilla email and explain to him that filtering out all messages with HTML in them is pointless. About half of NavList messages now include "plain text" and "html text" alternate views which means he's trashing about half of the message traffic. These alternate views are NORMAL in email in the year 2009, and the percentages are probably much higher in all email. Furthermore, the vast majority of email senders have no idea that they are sending an html view nor do they have any idea how to turn it off, if it's even possible in their email setup. It is possibly reasonable to filter out messages that include ONLY an html view and in fact most spam filters add a couple of points to their spam tally when they find a message with no plain text view at all.

I should get paid for this.