NavList:

Frank,

Thanks for another case for studies.

Time permitting, I will dig through your both examples here.

One immediate result, though : Yes, if the Moon altitude is sufficiently low - say between 10° and 20° - refraction may impact the time of occultation of a star by the Moon in some appreciable manner.

One of the reasons - maybe not the only one - for this difference in time is due to the differential refraction correction applicable to the Moon which is a finite distance body.

In our previous example you might be referring to, the Moon was too high for this effect - about 0.001" - to be significant. As earlier indicated, this effect just reaches 1.2" when the Moon is at the horizon.

As an example in this attachment recently re-published, from point A (bottom right of the sketch) the refracted star is just grazing the Moon, while it would be hidden by the Moon if they were no refraction. At the same instant of time, you would have to go to point B to see it grazing the Moon if no refraction.

One other extremely important factor is the Observer's altitude which I think we started addressing in our recent Lichtenstein Lunar. And in fact, the differential refraction correction is nothing but a variant of such paramount Observer's Altitude factor.

There could be other factors linked to just refraction. But I am not sure ... let me mull over it.

Kermit

PS : If the referenced attachment is not sufficiently readable, I can draw an other one.