NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Pointer star question
From: Alexandre Eremenko
Date: 2013 Feb 2, 16:57 -0500
From: Alexandre Eremenko
Date: 2013 Feb 2, 16:57 -0500
Just one remark. Stellarium is of course free and nice. But not reliable. I discovered this when I tried to see the recent event of Jupiter passing the Moon. Stellarium gave a totally wrong picture. I suppose because it had wrong Moon diameter, but did not investigate this further. So I would not rely on Stellarium, but read the coordinates from some reliable almanac. Alex. P.S. Some distributions of Linux (Fedora) have free software similar to Stellarium but much better. I used this 10 years ago when I had Linux on my laptop. It was especially useful for star distances. You click in a star and drug to another star. And it shows the distance. (Not corrected for refraction). It also had bugs though. A. > Looks like the distance from Merak to Polaris is 34.0699 degrees or 34° > 4' 12". This is the value for today without refraction. You can calculate > this if you know the stars' coordinates in RA (or GHA or SHA) and Dec. Let > me know if you're interested. You can read out coordinates from the free > software Stellarium (available from stellarium.org). While Stellarium has > some bugs, you can usually count on things like stellar coordinates. Just > click on each star, and the exact coordinates are displayed in the upper > left. There is also an angle-measuring tool available in Stellarium and > with careful clicking and zooming in and out, you can measure angles > between stars with an accuracy of at least 1' of arc. > > This star-to-star distance will vary slightly during the year due to > aberration, and it will vary significantly with the stars' altitudes due > to refraction. For example, if you're in latitude 41 N and the Dipper is > low in the sky with Merak almost directly below the pole star, Polaris > will be lifted by refraction by 1.1 minutes of arc while Merak (at an > altitude of about 7 degrees) will be lifted by about 7.3 minutes of arc so > the angular separation will be reduced by 6.2' to 33° 58.0'. If instead > Merak is high above Polaris, then the distance will be 34° 3.4' reduced > by refraction by only 0.8'. In the latter case, we're nearly in the > situation where the change in distance due to refraction follows the > simple rule "0.1' for every 5 degrees of distance" which applies with good > accuracy for any orientation of the pair of stars and any altitude as long > as both stars are above 45 degrees altitude. > > -FER > > > ---------------------------------------------------------------- > NavList message boards and member settings: www.fer3.com/NavList > Members may optionally receive posts by email. > To cancel email delivery, send a message to NoMail[at]fer3.com > ---------------------------------------------------------------- > > > > > : http://fer3.com/arc/m2.aspx?i=122231 > > >