iridium flare confusion

From: Peter Kok (kok_peter@hotmail.com)
Date: Wed Oct 16 2002 - 15:34:36 EDT

  • Next message: Bjorn Gimle: "Re: iridium flare confusion"

    Hello there-
    
    I seem to be having trouble identifying two iridium satellites. Iridflar 
    calculated the following predictions:
    
    Latitude:  51.98300  Longitude:    4.46700  Altitude:    -5.0 m
    Time Zone: UTC  +2.0 h
    
                               Iridium Coordinates  Range   Sat   Solar     
    Flare      Peak  Std    Maximum Flare   Bearing
    Ir# S    Date    Local Time Azm El   RA   Decl  (km)  N Ill Azm  Elev M 
    Angle  Mag  Mag  Mag Latitude Longitude  (km)
    -----------------------------------------------------------------------------------------------------------------------
    21  ? 2002-10-14 20:32:15.0 016 37  5h32  71.7 1096.6 A Lit 278 -15.8 L  
    3.38  1.9 -7.8  1.5  52.1200    5.4339  64.9 E
    66    2002-10-14 20:32:32.0 015 36  5h44  71.3 1210.8 A Lit 278 -15.9 L  
    2.85  1.6 -7.6  0.9  52.1424    5.3699  60.2 E
    
    This is what I saw:
    The first satellite appeared fairly early, heading north and flaring around 
    20:32:15, it was a bit brighter than I expected. This satellite only faded 
    slowly, and at a few seconds later the second satellite appeared, about two 
    degrees ahead of the first. It flared around 20:32:30, not as bright as the 
    first one. Actually, at the maximum of the second flare, the first satellite 
    was about as bright as the second. The second satellite faded quickly, but 
    the first was still clearly visible until 20:32:50.
    
    Everything nicely matches the predictions, but there's a problem. I've been 
    watching flares at this position in the sky for about a week now, and I 
    noticed the flare times are regularly 15 seconds before or after the 
    predicted times.
    
    How do I know for sure which satellite was which? (I'm not very good at 
    reading TLEs.) And what about the deviating prediction times?
    
    -Peter
    
    
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