ISS Transit Of Moon - Position Error

From: Philip Masding (
Date: Wed Jan 08 2003 - 15:51:59 EST

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    Hi everyone
    As Mike suggested below I have been using Tom Wagner's observation of the
    ISS transit of the moon to test the simulator. At first it predicted that
    the ISS would pass about 1 degree south of the moon just as Heavens Above
    did. Various other programs I looked at like Brent Bosharts SatTracker and
    Trackstar by Dr Kelso correctly predicted a pass across the moon. Eventually
    I worked out that the error was down to the calculation of the observers
    position. The problem is caused by using the observers geographical or
    geodetic latittude and not converting it to geocentric co-ordinates. At
    mid-latitudes that can result in an error of several degrees in the
    predicted RA DEC of a satellite. Once these corrections were in the
    simulator showed the ISS passing across the Moon.
    A good reference for the necessary corrections is
    and OCS part III in particular
    PS A new version of the ISS Simulator will be out soon including the Moon
    and greater acuracy of position and timing.
    ----- Original Message -----
    From: "G6GAK - Mike Tyrrell" <>
    To: "Philip Masding" <>
    Sent: Monday, December 30, 2002 7:03 PM
    Subject: FW: ISS Transit Of Moon
    > You could use this as a test of your moon/ISS positions in the
    > Mike
    > -----Original Message-----
    > From: Tom Wagner []
    > Sent: 30 December 2002 04:28
    > To: SeeSat
    > Subject: ISS Transit Of Moon
    > Hi all,
    > A few days ago I got a surprise announcement from Kevin Fetter, a Canadian
    > SeeSat member. He politely informed me that, if I was interested, in a few
    > days the ISS was going to cross the center of the moon as seen along a
    > a few km from my home. I more than gladly took up the challenge of
    > myself out of bed this morning after 4 hours of fitful sleep. I took my
    > telescope and a digital-8 video camera (capable of 4 lux) along. The sky
    > hazy but the moon was sharp as seen through my scope. At the time that
    > determined that the Station would pass it did, right where it was supposed
    > to! I could clearly see it cross both the dark AND sunlit parts of the
    > even though the Station itself was only a magnitude 1.6 (according to
    H-A ).
    > The moon was 23% illuminated and 25 degrees above the SE horizon. At 31x I
    > didn't detect any shape in the Station's image but I could tell that it
    > a small extended object.
    > I got the pass on video! Someday I'll get the time to make the video
    > available online.
    > H-A as we discussed in earlier posts did not accurately place the track of
    > the Station across the moon. It showed it passing about 1 degree south of
    > it. Much thanks to Chris Peat all the same!
    > The data I chose to use was as follows: 29 Dec 2002, 11:57:25.70,
    > 42.390, -92.318. That put me at the telescope at 5:57 AM out in a ditch in
    > the country. I'm glad the farm dog that started barking didn't come to
    > a look. I've been bitten before. To decide where to go I input the
    > coordinates into .
    > Thanks again Kevin!
    > Clear skies,
    > Tom
    > Iowa
    > USA
    > At home:
    > Latitude: +42.473513
    > Longitude -92.360413
    > Meters above sea level: 274
    > GMT -6
    > .....
    > -----------------------------------------------------------------
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