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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Antoine Couëtte
Date: 2023 Oct 19, 11:48 -0700
What a mess in the published dates, if not in the published times !
All in all, all 3 published occultations seem to concern one same event, i.e. happening on Oct 23rd, 1924.
With TT-UT = +23.7s, from Seagrave Observatory at N41°50.71' / W071°35.47' elev. +107m - also assuming same elevation of +107m above the WGS84 ellipsoid - with T=31°F and QFE=29.9" :
With refraction : Immersion at 10h57m58.3s and Emersion at 12h11m34.4s
Without refraction : Immersion at 10h57m58.8s and Emersion at 12h11m34.1s
The difference between refracted and unrefracted times is just inside my "blind computation time zone", hence I would surmise that refraction did not change anything at all here.
We probably would need Paul's Lunar Software to sort it out.
Now ... compared to the published times translated into current UT - i.e. if I am correct ... 10:58:24.5 and 12:13:42.5 - it looks like we find differences of 30 seconds for the Immersion time and over 2 minutes for the Emersion time. Certainly this is quite disappointing.
Could Astronomers not do better by these times ?
Well ... let's have a look at the observation from Donald B. Prentice - the only one to give us a correct date - who was observing from Providence and most probably from Ladd Observatory located almost at his doorstep at N41°50'15.6" / W071°23'59.26" elev. +69 m and assuming the same weather conditions as the ones prevailing at the nearby Seagrave Observatory.
He confidently indicates an Immersion time at 10h58m23.0s while I am findind 10h58m20.2 s. He certainly nailed it here !
As a comparison, by the same period André Danjon lists for η Tauri an Occultation seen from Paris on Jan 14th, 1935 for which - reworked with modern tools - the difference is under 10 s of time. Same for 27 Arietis seen from Strasbourg on 20 Dec 1931 where the difference for Occultation is under 5 s of time by modern computation software.
As an overall result, the Immersion time from the Ladd Observatory is excellent, while the results - Immersion and especially Emersion (to be done under adverse conditions as per Donald B. Prentice who did not even risk himself at it) - from the Seagrave Observatory are certainly quite disappointing. Did they have a reliable time keeper there ? Or maybe that is just a typo, one more ...
Back to refraction, at least in this example, I do not think it changes the Occultation and Emersion times in any appreciable manner. If it ever did, that would most probably be [well] under one second of time.
Kermit
