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Good Day to you Geoff,

Thank you for your reply.

I am going to "elaborate" on your last example taken from it, i.e. Refracted and Unrefracted disappearances of the Moon at Ladd Observatory, as it includes both refracted and unrefracted times of the same phenomenon.

Your remark is right : in this SWE example, both refracted and unrefracted Moon SD's show up as [almost] identical : 932.62905" for the refracted SD and 932.6295" for the unrefracted SD. This cannot be so in the real world. In other words, both results are not compatible together.

As can be expected and again, the right SWE published value here is the refracted SD, while the unrefracted SD should be somewhat "bigger".

I have carefully computed the oblique SD contraction due to refraction and I find it to be at -0.2993" where I trust at least its first 3 digits to be meaningful.

Hence the SWE published refracted SD should be increased by +0.2993" to match the actual unrefracted SD.

Since the unrefracted distances are decreasing at a rate of -0.3334"/s of UT time , the actual unrefracted occultation occurred (0.2993/0.3334) s = 0.898 s earlier than the published SWE unrefracted time, i.e. at a Corrected unrefracted UT = 10:58:21.78 - 0:00:00.90 = 10:58:20.88 to be compared with your SWE refracted result at 23.10.1924 10:58:20.91 .

Again this SWE derived 0.03 s difference between refracted and unrefracted times confirms my earlier statement : " (2) - The effect of refraction on the times of both Immersion and Emersion is under 0.02 s of time. ".

In other words, I would conclude that, if any, the effect of refraction onto stars occultation times by a [Spherical] Moon, stays under a few hundreths of a second of time. The only factor remains the Parallax induced refraction earlier addressed which is most often insignificant, while under extreme cases - e.g. grazing occultations - it can (could?) become significant.

Kermit