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Alex

> You are welcome to use my script for this.
> I think we checked that my Gnumeric script
> works with your Excel, or did we verify vise versa?

We verified that your operating system (free linux flavor of unix if I
recall) and box could read a hybrid Mac/PC CD burned on a Mac (OS 9.x), and
that your Gnumeric application opened the Mac Excel spreadsheet without
complaining, and did not choke on all the "IF" arguments in my spreadsheet.
It appeared to handle all the calculations flawlessly.  Note I use absolute
values for declination, latitude, longitude etc. and let IF arguments pick
the correctly signed value/cell based on input of North, South, East, West,
v & d incremental correction by body, etc. Only v & d values are signed on
entry. It also calculates Zn from Z with IF arguments.  I did not play with
changing the N, S, E, W inputs on your box to see if your program would
honor the IF statements if parameters were changed.  I don't know whether
you played with the provided CD to determine if it would work across the
board.

We have not tested to determine if my Mac will read a CD from your machine,
or if Excel will open your Gnumeric files with or without translation.

If I recall, several of the of the list members use both Mac and PC
platforms.  Any input as to the application and platform compatibility would
be appreciated by me.

> Or you want the relevant trig
> formulas, to program them yourself?
> They are easy and I can post them (if there are other
> interested people) or email them to you directly.

Would like to try both your Gnumeric files and have the formula.  If others
request, go ahead and post.  Otherwise we can exchange over adult beverages
when you return from the Great White North and I return your copy of Meesus
etc. (before it does further damage to my aging gray matter and gets me
invitations to  from the list ;-)
>
> (I believe these formulas are also in Chauvenet, but
> cannot check now because I am in Canada, coming back
> in a week.
>
> On your other question: BOTH star altitudes have to be corrected
> for refraction.

Understood.  Working towards understanding how, as you have surmised.

Thanks

Bill
>
>
> On Fri, 11 Mar 2005, Bill wrote:
>
>> Meesus et al gave formulas for calculating star-to-star angular distance
>> given declinations and SHAs.
>>
>> I am looking at the reverse case.  Measuring the angular difference between
>> two stars at different altitudes.
>>
>> For discussion purposes only, I suggest the following theoretical example:
>>
>> Star 1 Hs (altitude)   50d
>> Star 2 Hs (altitude)   10d
>> Measured distance      56d 34'.1
>>
>> Given STP and 0 dip and IC, and adjusting for vertical refraction:
>>
>> Star 1 Ho              49d 59'.2
>> Star 2 Ho              09d 54'.7
>> Angular distance        ?
>>
>> The vertical component of the difference between the two has gone from 40d
>> to 40d 04'.5.  Now the distance measured along the Hs diagonal will be less
>> than the distance between the Ho positions in the above example (ignoring
>> other factors).
>> Correct?
>>
>> My next query, will there be horizontal refraction as well?
>>
>> In Meesus's chapter on refraction he gives an example of the reduction of
>> the Sun's vertical observed measurement when near the horizon due to
>> refraction.  He then states, "...the horizontal diameter of the solar disk
>> is very slightly contracted by reason of the refraction.  This is due to the
>> fact that the extremities of this diameter are raised along vertical circles
>> that meet at the zenith."  He goes on to mention Danjon, "...writes the
>> apparent contraction of horizontal diameter of the Sun is practically
>> constant and independent of altitude, and  that this contraction is
>> approximately 0".6."
>>
>> Perhaps I am comparing apples to oranges, but the star viewed through the
>> horizon glass is straight on and would not exhibit horizontal refraction?
>> As the other star is viewed at an angle (relative to the first) through the
>> index and horizon mirrors, would there be horizontal refraction affecting
>> the horizontal component of the diagonal between the two?  If so, how would
>> that correction be calculated?
>>
>> Confused in Indiana
>>
>> Bill
>>

   

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