Re: I saw ISS :-)

From: Michael McCants (mmccants@jump.net)
Date: Mon Apr 14 2003 - 14:26:13 EDT

  • Next message: Tom Wagner: "ISS solar transit on 4-15-03"

    Thomas Fly wrote:
    
    >Ed Cannon wrote:
    >
    >> I got the binoculars on it and attempted to click the beginning and end of
    >> the transit and got these times, plus or minus about 0.05 using WWV:
    >>
    >>  1:56:56.70 April 14 - begin transit
    >>  1:56:57.56 - end transit
    >
    >Better 4 seconds late than 17 seconds early, I guess!
    
    I ran an old version of "ephem" for this lat/long/time and got:
    
    Moon coordinates 11 Hr 13.9 Mn, 10.38 deg Dec (2000)
                     Alt 51.13, Azi 113.83
    
    I ran my version of SeeSat 4.0 with the tles:
    
    1 25544U 98067A   03104.44047454  .00016643  00000-0  22273-3 0  8910
    2 25544  51.6348 340.4225 0006548  20.6391 337.4675 15.58129290251053
    
    (There was one elset recently with both drag and mean motion too large.)
    
    and got
    
    ISS              2003 APR 14 (coordinates 2000)
     time    alt    azi      R.A.    dec  range   hgt   sun
    0156:54 53.10 112.27  11 11.61  11.97   303   246   3.9
    0156:55 52.45 112.83  11 12.98  11.31   305   246   3.8
    0156:56 51.80 113.37  11 14.33  10.67   308   246   3.8
    0156:57 51.17 113.88  11 15.66  10.03   310   246   3.7
    0156:58 50.54 114.38  11 16.96   9.41   313   246   3.7
    0156:59 49.91 114.85  11 18.24   8.79   315   246   3.6
    
    The alt/azi matches at 1:56:57.0, but the RA and Dec interpolated
    to 1:56:56.3 are 11 Hr 14.7, 10.47.  That would imply a pass that
    is just grazing the moon.
    
    This indicates that Ed's times are certainly within 1 second and possibly
    much closer than that.
    
    >It seems like .86 seconds is a bit too long, though.
    
    ISS motion 1.3 Mn RA = 0.31 deg/sec, -0.63 Dec deg/second
    
    RMS = 0.70 degrees / second.  Transit time for 0.5 degrees is 0.71 seconds.
    
    >and traveling at around 5 miles per second, that's 1/50 radian per second,
    >so the transit actually should have lasted less than .5 second.
    
    But the "projection effect" obviously lengthens that time.
    
    Mike McCants
    
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