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Re: Star to star angular measurement, beginner
From: Alexandre Eremenko
Date: 2005 Mar 14, 19:20 -0500
From: Alexandre Eremenko
Date: 2005 Mar 14, 19:20 -0500
Bill, as no one else seems to be interested, if you can wait till next week, I will just hand you the formula on a sheet of paper rather than type it in e-mail. (I suppose your computer has no TeX installed. TeX is a special soft for typing formulas, used by mathematicians). Alex. On Mon, 14 Mar 2005, Bill wrote: > 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 > >> >