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Dear Paul,

As a complement to my first and recent reply to your previous remark :

QUOTE

"it's not possible for Horizons to calculate refracted semidiameter. That depends on the position angle on the limb. But there's no way to input that angle to Horizons. "

UNQOTE

(1) - I fully agree in general with your statement because computing a refracted semidiameter requires a position angle.

I am not familiar at all with JPL Horizons and have not studied its User's notice.

Nonetheless, JPL Horizons does "publish" a series of refracted SD's which apparently are quite accurate and reliable.

The best explanation to this fact is that the "published" refracted SD's are [implicitely] computed alongside the respective lines joining Sun Center and Moon Center for each time of the successive computations - every half a second - and for/from the given position.

It can not be differently.

(2) - This brings up another point :

It would be interesting to broaden this discussion and invite on board one of the Engineers and Software developpers who worked at JPL Horizons so that we can hear their viewpoint here.

Frank ???   :-)

Kermit