# NavList:

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

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
Re: Angular Distance Between Stars By Camera and Sextant
Date: 2012 Sep 18, 14:57 -0400

Marcel

The USNO issues "The Astronomical Almanac"  US Gov't Printing Office.  My last copy was from 2009.

Alkaid (Bayer 85 Eta Ursae Majoris SAO 44752 HIP 67301) in that 2009 Astromonical Almanac as RA 13 hours 47 minutes 54.9 seconds Declination +49 degrees 15 minutes 58 seconds.

Alioth (Bayer 77 Epsilon Ursae Majoris SAO 28553 HIP 62956) in that 2009 Astronomical Almanac as RA 12 hours 54 minutes 26.7 seconds Declination +55 degrees 54 minutes 30 seconds.

You estimated that we would need data to 1/100 moa (minute of arc) in order to properly calibrate the arc.  Do these values meet your criteria?

Kind Regards

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

----------------------------------------------------------------
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
----------------------------------------------------------------

Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)