determining coord distances for H-A predictions

From: Tom Wagner (sciteach@mchsi.com)
Date: Wed Sep 28 2005 - 22:18:14 EDT

  • Next message: sciteach@mchsi.com: "Re: determining coord distances for H-A predictions"

    This post has to do with using coordinates to try to predict where to best 
    observe iridium flares.
    
    
    
    I am now teaching 8th grade science as well as all high school science and 
    have astronomy and satellites as part of the curriculum in 8th grade 
    science. I introduced the young students to Heavens-Above and am trying to 
    set up a way that I can quickly predict a coordinate to go to using a GPS 
    unit to see -8 flares. A few of the students are now hooked ion using GPS 
    technology too.
    
    
    
    Tonight I wanted to see what longitude (with two latitudes) I needed to add 
    into my GPSr as a one-legged route so that I could, anywhere along that 
    line, see a -8 iridium flare. It was only some 6.8 km E of my computer desk. 
    [I get a reading on my GPSr in the upper room of my house even though it's 
    indoors, I discovered.]  Other than going to H-A I went to a website that I 
    often go to get an idea as to how much of a degree so many Km would be and 
    vice versa. However, I seemed to have had some trouble. As a result I began 
    to simply move the longitude eastward on H-A while checking the same flare 
    till I got a point with a -8 flare. However, I would rather be able to make 
    a conversion from km to fractions of a degree for my latitude so I could see 
    what H-A says and make a quick adjustment to a particular longitude and take 
    off using my GPS as a guide.
    
    
    
    The thing that is puzzling me now is that the website 
    http://jan.ucc.nau.edu/~cvm/latlongdist.html where I customarily get my 
    distances between two points seems to be giving me some lousy data in one 
    instance at least. I was suing that website to try to get some data about 
    how many km are in a certain amount of longitude at my latitude. I found 
    that when I plug in two coordinates in decimal degrees, varying only the 
    longitude, I get an answer that seems wrong then when I type in the exact 
    equivalent in degrees, minutes & seconds for the two points I get quite a 
    different result. The degrees minutes seconds mode at the above website got 
    me a value that was the same as what I got here: 
    http://www.fcc.gov/mb/audio/bickel/distance.html when using the same two 
    coordinates.
    
    Here is what I got at the first website (the edu/ one) when I plugged in the 
    decimal values given here: Distance between 42.473567'N  92.360250'W and 
    42.473567'N  92.526917'W is 0.3092 km. Here is what I got at the SAME 
    website when I typed in the given DMS values: Distance between 42 28' 25"N 
    92 21' 37"W and  42 28' 25"N  92 31' 37"W is13.6844 km.See the 
    difference?This is what I got at the second website (the gov/ one) with the 
    DMS values shown:  Distance between N Latitude 42 28 25.00, W Longitude 92 
    21 37.00 (Point 1)and N Latitude 42 28 25.00, W Longitude 92 31 37.00 (Point 
    2) is 13.668 kilometersNow that's close to the DMS value from the other one.
    
    
    
    Can someone tell me of a website that I can go to in which I can use decimal 
    degrees, like H-A uses, to get reliable distances per degree etc?
    
    
    
    Thanks!
    
    
    
    Tom  Iowa  USA
    
    
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