GPS for ISS transits and iridium flares

From: Tom Wagner (
Date: Thu Feb 12 2004 - 13:47:51 EST

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    Note: This is the 3rd time Iíve 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. Itís 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 Flyís 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. Iíll 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 Denisí 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!  
    Tom  Iowa  USA + + +
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