# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

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Re: Angular Distance Between Stars By Camera and Sextant
Date: 2012 Sep 18, 14:39 -0400

That was my understanding as well.

Andres - Do you set this term to zero (0) for the iteration?

On Sep 18, 2012 2:36 PM, "Greg Rudzinski" <gregrudzinski@yahoo.com> wrote:

You are correct that dip is of no interest for star to star distance. A calculated Hc to the nearest minute is more than good enough to figure refraction corrections. Where dip comes into play is in star to Moon distance when observed altitudes are taken from the natural horizon. Apples and oranges.

Greg Rudzinski

[NavList] Re: Angular Distance Between Stars By Camera and Sextant
Date: 18 Sep 2012 13:48
If I am measuring star-to-star distances, then I fail to understand how dip of the horizon is important

Shouldn't the calculated altitude of the two objects be sufficient to determine the refraction?

Dip would be part of reducing the measured altitude, no?

Best Regards

On Sep 18, 2012 1:04 PM, "Marcel Tschudin" <marcel.e.tschudin---com> wrote:
Andrés, you clarified

On Tue, Sep 18, 2012 at 7:08 PM, Andres Ruiz <navigationalalgorithms---com> wrote:

Hc = Hc( B, L, Dec, GHA )
Z = Z( B, Dec, Hc, LHA( L, GHA ) );
iterate to find Hs ( Hc = Ho = Hs + IE - dip - R )
Ha = Hs + IE - dip;
R = Refraccion( Ha, T, P );

Ok, yes, I completely forgot that your program is for verifying sextant observations and does therefore more than just calculating the difference in star coordinates. However, since both star positions contain the same dip this should have no influence on the calculated star distance. The difference of 0.4 moa still waits to be understood.

Marcel

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