Re: Satellite visual magnitude equations

From: Ed Davies (edavies@nildram.co.uk)
Date: Thu Apr 26 2001 - 15:07:48 PDT

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    Robert Matson wrote:
    > Mag = Std. mag + 2.5*LOG((1600/1000)^2)   -or-
    > Mag = Std. mag + 5*LOG(1600/1000)
    >     = 5.5 + 1.02 = 6.52
    > .... 
    > A simplified general equation for object at 90-degree
    > phase angle is:
    >
    > Mag = Std. mag - 15 + 5*LOG(Range)
    >
    > where Range is in km.
     
    Jonathan Wojack replied:
    > I'm just trying to understand the math involved - where does the -15 come
    > from?
    
    Thanks to both of you for this most "illuminating" (sorry) discussion.
    
    I think Robert has answered all of the questions except this last one
    of Jonathan's so I'll venture to point out that 5*LOG(1000) = 15.
    Subtracting 15 from the multiplied log value is the same as dividing
    the actual range by the standard range (1000km) before taking the log.
    
    Ed.
    
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