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    Re: Heliacal rising - definition?
    From: George Huxtable
    Date: 2011 Aug 18, 21:07 +0100

    I'm surprised that nobody has mentioned Brad Schaefer's work in this
    context (and in many other related fields concerned with atmospheric
    effects on arriving light).
    
    A search for Schaefer, combined with extinction, should take you to
    anything you need to know.
    
    George.
    
    contact George Huxtable, at  george@hux.me.uk
    or at +44 1865 820222 (from UK, 01865 820222)
    or at 1 Sandy Lane, Southmoor, Abingdon, Oxon OX13 5HX, UK.
    ----- Original Message -----
    From: "Apache Runner" 
    To: 
    Sent: Wednesday, August 17, 2011 4:44 PM
    Subject: [NavList] Heliacal rising - definition?
    
    
    |I have a question: can someone define heliacal rising in a quantitative
    | fashion?   The reason I ask is that I'm interested in writing a piece of
    | code to identify heliacal risings, but when I think about the
    | implementation, many questions arise.
    |
    | Roughly speaking, the heliacal rising is the first time a star is visible
    | just before sunrise.    If I think about what might actually be visible
    at a
    | given latitude, this seems to me to depend on the magnitude of the star,
    and
    | even atmospheric effects, and even the height of the observer, if I were
    to
    | get persnickety.
    |
    | On the other hand, if I define some group of stars with a magnitude
    greater
    | than X, and say it's 'first visible' before local sunrise at, say 6
    degrees
    | above the horizon at the start of astronomical twilight, I can get a
    precise
    | definition that I could implement in a piece of code - although this
    would
    | probably yield some stars that would be several days past the 'first'
    | observation.
    |
    | The latter definition is straightforward to implement, while the former
    is
    | difficult for me to see how it would work.
    |
    | Any thoughts?
    |
    
    
    
    
    

       
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