Welcome to the NavList Message Boards.

NavList:

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

Compose Your Message

Message:αβγ
Message:abc
Add Images & Files
    or...
       
    Reply
    Re: Star to Star with Stellarium
    From: Frank Reed
    Date: 2012 Aug 19, 08:47 -0700

    Luc,

    A few years back I discovered a rather neat mathematical cancellation that makes it easy to correct star-to-star distances for refraction whenever both distances are above 45 degrees, as in the example you've described. Refraction lifts all stars. For higher altitudes, the refraction is nearly proportional to the distance from the zenith. But mathematically, when you contract distances in proportion to the distance radially from some center, you're contracting all distances, whether aligned radially or not, in a simple proportion. For standard refraction, it's "one part in 3000" or equivalently 0.1' for every 5 degrees of distance. And again, this applies regardless of the orientation. If the un-refracted distance is 10d 0.0' then the refracted distance is 9d 59.8' whether one star is directly above the other, or they're both at the same altitude, or any orientation in between. All distances are compressed by the same amount. This only works when both stars are above about 45 degrees. Below that altitude, the refraction changes in a more non-linear fashion so you need to do a more involved calculation.

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

       
    Reply
    Browse Files

    Drop Files

    NavList

    What is NavList?

    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)

    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site
    Visit this site