Re: Iridium : observing project , Iridial constellation

From: Gerhard HOLTKAMP (
Date: Tue May 31 2005 - 14:57:40 EDT

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    Walter Nissen wrote:
    >"How far North do you have to be to see more planes simultaneously?".
    For a minimum satellite elevation of 10 you would have to be higher than 
    latitude 75 to see all Iridium planes simultaneously. For a minumum 
    elevation of 20 it would be 80.5. The northernmost town with a daily 
    scheduled air service (I think) is Longyearbyen in Svalbard (Spitsbergen) at 
    78.15 which offers you 15 minimum elevation on all Iridium planes. But 
    except for very bright Iridium flares you would not see much during the 
    summer time due to the midnight sun. Up there the time to do your 
    observations would be winter. 
    Taking this site (which by the way is about as far North as McMurdo in 
    Antarctica is South) and doing a few calculations I found that even in 
    mid-winter there are certain times of the day when illuminated satellites 
    from all six planes would be high enough in the sky simultanously to be 
    observed (in different directions, of course, and with binoculars as most of 
    them would not flare at the time). In fact, you could see every single 
    satellite of the Iridium constellation within a 100 minute period! At other 
    times of the day the section visible from the observation site of one or the 
    other plane might not be illuminated. An observer directly at the Pole could 
    see satellites from all planes all the time throughout the day.
    Gerhard HOLTKAMP
    Darmstadt, Germany
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