Re: GPS for ISS transits and iridium flares

From: John Locker (
Date: Thu Feb 12 2004 - 14:36:50 EST

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    Hi Tom ,
     I have been using  this technique for the past few months .
    I carry out as much research as I can prior to the transit time , making a
    dummy GPS run before hand if need be.
    By doing this I can locate a number of sites within the "corridor" .
    In addition I make use of  maps and aerial photos of the possible locations
    ( Memory Map navigator ) , loading  photos and large scale maps into my GPS
    PDA....especially if I am not familiar with the topography.This can be quite
    handy .
    I reckon that using the GPS , subject to local  conditions , can usually get
    me within a 100 feet or so of my prefered location.
    All good fun , and a few hours preparation can mean the difference between
    seeing a spactacular transit........or nothing at all !
    ----- Original Message ----- 
    From: "Tom Wagner" <>
    To: <>
    Sent: Thursday, February 12, 2004 6:47 PM
    Subject: GPS for ISS transits and iridium flares
    > Note: This is the 3rd time I've tried to submit this message, this time
    from school, the other two from home. The first two did not seem to go
    through. Hopefully this message will not suddenly show up three times!
    > +++++++
    > I have an idea that will enhance the observing of ISS transits and other
    things that require exact placement of people on the globe. It's so basic
    that it may have already been discussed on this list. Then again, for all I
    know, many of you may already use it.
    > I recently purchased a GPS receiver and, among other things, plan to use
    it to find an exact place where I need to be to see centered ISS solar and
    lunar transits. The problem has been, lately no transits have been occurring
    at a time when I can watch or they have been too far away!
    > My technique for placing my two feet in the right spot follows. Into my
    GPS unit I will plug in the two most distant coordinates I get from Tom
    Fly's latest transit prediction. Then using those two coordinates I will
    make a "one-legged route." The route will be represented as a single line
    between those two points. I will drive toward any place on the line then
    when I get near it I will change the scale of the GPS screen until I get to
    a maximum resolution. I'll move around until the little arrow icon showing
    my current position is centered over the route line. At that point I should
    easily be within 50 feet and probably much closer to where I need to be to
    see a centered transit. The time of transit may not be perfectly known using
    this simple technique but I should know it within a few seconds, especially
    if I bring a list of times along the route then estimate. I am thinking that
    this method would be a more precise and less bothersome method trying to
    find a very specific!
    >   location on a map. As a bonus many GPS units can be downloaded with or
    already have road maps in them. I would imagine that once Tom gets the
    predictions up for ISS transits of planets, using a GPS unit will almost be
    a must!
    > My other idea may be a bit too much of a bother for most iridium flares
    but certainly not for Denis' transit of Saturn flare that he just wrote
    about! What I have done is this. I made 3 shortcuts to H-A. One is for my
    home base. The other two are for locations 0.2 minutes (about 13.8 miles) in
    latitude N and S of my place. I then check Heavens-Above (H-A) for my
    location and when I see that there is going to be a -8 flare within say, 10
    miles of home, I use H-A to get the coordinates for the point S and the
    point N of my home. Those two points then allow me to create a one-legged
    route. Before the flare occurs I drive to any point along the line. As far
    as the time goes I know that the flare will be within a few seconds of the
    time for either extreme along the route.
    > A few weeks ago I started a local "geocaching" e-mail group.[Geocaching is
    a whole other story.] On that list I have been posting ISS transit
    coordinates and -8 iridium flare coordinates as well. That way other
    "geocachers" can have something more to do during times that our geocaches
    are buried under the snow. They can watch for satellites!
    > Regards,
    > Tom  Iowa  USA + + +
    > -------------------------------------------------------------------------
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