Re: almost time for the ISS marathon

From: Bjoern Gimle@GlocalNet (Gimle@GlocalNet)
Date: Wed May 14 2008 - 16:10:08 UTC

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    Marathon == constant sunlight??
    I know the constant sunlight period has implications for ISS
    temperature and for STS scheduling.
    But for an observer, the marathon is when the largest
    number of consecutive passes are sunlit above horizon
    (and visible at night).
    IE the fraction of the orbit that can be above horizon for him is sunlit.
    Not quite, since at 349 km (and 6370 earth radius) we can "see"
    ISS at 18.5 degrees "distance", ie 18.5 below our latitude.
    But that is only in the S - to see as many passes as possible
    in sequence you must have CULMINATION just above horizon.
    So the marathon start is when the apex is as far east of you
    as possible, with the track passing 18.5 deg away, the end
    after the westernmost corresponding apex.
    At 59.05 GEOCENTRIC latitude I can "see" 5 passes,
    if it is sunlit above 44N (and I can see it though the Sun may be above 
    At 41.1N (or 41.1S) the number of passes has risen to 8.
    It must be sunlit above latitude 29.
    South of about 32.3N (north of 32.3S) a marathon is impossible,
    but you may need to be at 33.1 in case the apex of the middle pass
    falls close to the meridian.
    You can still see 8 passes if it is sunlit at latitude > 20.8 degrees
    If you wish to check my computation, or compute for a
    different latitude, I can send my .xls spreadsheet.
    (Assuming circular orbit and spherical Earth, free horizon)
    SkyMap shows only penumbra May 21 14:35 UTC
    Track16 has the shadow gone May 22, about 02:00 UT
    >> ----- Original Message ----- 
    >> Between roughly 6 UTC ( May 21 ) to 15 UTC ( May 23 ) the
    >> ISS won't pass through the earth's umbra.
    >> So between those times, it will be in constant sunlight.
    >> So get ready for seeing the ISS pass by, a few times during the night.
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