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    Re: Can you work a Polaris problem just like any otherstar?
    From: Geoffrey Kolbe
    Date: 2014 Jan 7, 06:41 +0000



    On Sun, Jan 5, 2014 at 9:42 PM, Frank Reed <FrankReed{at}historicalatlas.com> wrote:

    Greg, you asked Geoffrey:


    "would you think you could see Polaris during the day at 40 deg Lat?"

    You can, but you need magnification and a very clear sky. Magnification increases the contrast of the sky. It makes the background blue deeper so it's easier to see a second-magnitude star like Polaris. If the sky is clear blue, and you aim a telescope with magnification 25x or better at the right coordinates, you can see Polaris in daylight.

    Geoffrey, what has your experience been? Have you seen Polaris in daylight in the desert? How about in Scotland (higher Polaris altitude but presumably lower transparency).

    -FER

    I was doing some experiments on pyramid alignment in Egypt some years ago and had nothing much to do during the day as the experiments were a night time activity. So, one day, I decided to look for Polaris through my theodolite telescope. I used a timed observation of the edge of the sun to calibrate the azimuth, which I knew from experience would be correct to a minute or so. And I knew my position, so setting the altitude of the scope was trivial. The sky was pretty blue, as it usually is in Egypt, but Polaris just was not there. 

    The altitude of Polaris at that location would have been about 25 degrees, and I was in the Nile valley looking North over the smog created by 80 million Egyptians who also lived in the Nile valley as it headed North from where I was. So, even with a "blue" sky, the seeing was not expected to be great. At night, the 1st magnitude stars I was looking at in much the same direction were visible, but dimmer than I had expected, frankly. Too, the theodolite was a relatively cheap Russian job made of aluminium, which I use for this kind of jaunt because it is light (weighing in at just 2 kgs) and plenty accurate enough for what I needed. If I had been using a "good" theodolite with decent optics, it might have been a different story.

    Back here in Scotland where I live, Polaris is at an altitude of 55 degrees (my latitude) and you just cannot get your eye behind the scope when it is cranked up at that angle. That is the limitation of the usual 'transit' type of theodolite, you are really limited to objects with altitudes of 40 degrees or less for viewing that is comfortable, let alone possible. So called 'broken' theodolites like the Wild T4, where there is a right angle bend in the telescope, are what is really needed for celestial work. But the Wild T4 is accurate to a tenth of a second of arc and has a price tag to match - when they are available. Theodolites used for tracking weather balloons are also 'broken' type theodolites, and they appear quite regularly on ebay, but they are usually graduated to read in tenths of a degree and that is just not good enough for celestial work.

    So, I have not personally seen Polaris during the day. But, it is a pretty standard method in the surveying literature so I guess it is/was a pretty routine procedure.

    Geoffrey Kolbe



    --
    Dr Geoffrey Kolbe, Riccarton Farm, Newcastleton, Scotland, TD9 0SN
    Tel: 013873 76715
       
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