NavList:

To the specific Attention of Paul W. Jackson, and Greg Redzinski :

Dear Paul and Greg,

1 - Paul, in [NavList # 13785] you informed our NavList Community about your most recent "Venus daylight observations" taken in the "maritime suburb" of Auckland, Nouvelle Zélande on Sep 09 th (local date). You subsequently published (Thanks again) one such observations under the form of a "picture" in your post [NavList # 13795] 11 Sep 01:31.

Through carefully looking at your picture, I think that I can read the following note : "Result by Navigator = 0.1 NM towards 048°"

And BTW, this note makes sense since this specific "0.1 NM" intercept seems to be the one you initially quoted in your very first post on this subject [NavList # 13785]. Am I right ?

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2 - In my post [NavList # 13808] 11 Sep 10:22, and because I had difficulties to read it, I "transcripted" your "pictured data" into plain typed figures so that everybody -yourself included- could check that this transcription is correct. Using these transcripted data, I then published an intercept of 1.2 NM Towards Venus, with an Azimut of 047°9.

For the sake of being more comprehensive - so that anybody can crosscheck my computations - for the time of your observation I am using the following apparent coordinates for the Center of Light of Venus :

GHA = 163°01'96 and
Dec = S -14°57'32

NOTE 1 : I compute the "Center of Light" apparent Coordinates of Venus from its "Geometrical Center" apparent Coordinates and by subsequently applying a correction of +0'153 to its GHA and of +0'069 to its Declination.

NOTE 2 : Such apparent coordinates should both be accurate to better than 0.05'.

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3 - In your post [NavList # 13809] 11 Sep 2010 11:28, Greg you published an intercept value of "1.3 NM towards" through "using a natural horizon". Greg, did you use the same starting data as the ones I used in part 2 just hereabove ?
It would seem that yes, since our independently computed results are extremely close and their (subtle) difference certainly is not significant. I too was assuming "natural horizon" exactly as you did.

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4 - Then in your posts [NavList # 13814] 11 Sep 2010 01:47, and [NavList # 13815] 12 Sep 2010 02:38 Paul you kindly replied to each of us.

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5 - However, Paul, I still have one query rather similar to the unanswered query Greg asked you in 3 hereabove.

How can we reconcile both our similar results ("1.2 NM towards" and "1.3 NM towards" intercepts ) with the "0.1 NM towards" intercept you seem to have achieved with "Navigator" ? It probably deals with the way of implementing the "dip" or "dip short" correction, whichever way you had to perform it. Actually, when looking on Google Earth, you were apparently quite close from getting a "obscured" horizon due to the western tip of Rangitoto Island. Which kind of horizon did you get ? obscured ? unobscured (= "natural" in the sense quoted hereabove)?

Any additionnal clarification or further explanation from your side would be most welcome.

One last question : were you not using an ASTRA III (B?) Sextant for this shot ?

Thank you again, and

Best Regards from

Antoine

Antoine M. "Kermit" Couëtte

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