Re: Transit of the sun by ISS from SoCal, Nevada, etc.

From: Ralph McConahy (rmcconahy@earthlink.net)
Date: Sat Apr 20 2002 - 15:51:46 EDT

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    Rob Matson wrote:
    
    > The International Space Station is going to transit
    > the sun on Saturday morning, April 20th, as seen
    > from a narrow swath of land in southern California...
    
    Last night I figured that I'd see how close the center line was to where I
    live, so I got the latest TLE for the ISS (epoch 02109.82334568) and
    behold!, SkyMap indicated that as seen from my own back yard, the transit
    would go right through the center of the sun. This morning, however, I
    downloaded:
    
    ISS
    1 25544U 98067A   02110.45923306  .00036084  00000-0  48365-3 0  3327
    2 25544  51.6392 342.9735 0006692 345.0510  74.1641 15.57591621195024
    
    and discovered that the transit was now slightly missing the sun as seen
    from my yard. Again using SkyMap, I calculated Lat/Lon for two places where
    the new center line will be. I plotted those on a computer map then extended
    the line to a place near roads. It was only about 3 miles (~5 km) east of me
    at 34.8838N 117.0547W ~650m.
    
    About 30 minutes before the transit I set off with a Meade ETX-90 telescope
    with a doubled-over piece of silverized Mylar over the front for a solar
    filter, a small table to place the scope on, a GPS receiver, a stopwatch,
    and a shortwave radio for WWV.
    
    The wind was blowing (welcome to the desert) and at one time it blew my
    glasses off the table (I don't use them to look through the scope) and onto
    the ground; fortunately no damage. One other problem was that the sun was
    still a little too bright in the scope, but I solved that problem by making
    a poor-man's neutral density filter by holding a pair of clip-on sunglasses
    between my eye and the ocular.
    
    Using the TLE above, SkyMap predicted the transit at the center of the sun
    at 18:39:27.5 but it occurred about 0.5 seconds earlier--about right on the
    :27 second mark. It was on track, right through the center of the sun.
    
    I used an ocular that gave me about a 0.75 FOV. I had no idea what to
    expect. The transit itself was FAST, hardly 0.2 seconds long. The ISS was
    even smaller than I'd expected (birds flying in front of the moon appear
    much larger in the same scope). I can't say that the visual experience was
    all that much to get excited about, but the fun part was planning it,
    setting up, and simply knowing that it can be done.
    
    Thanks Rob for the heads up!
    
      Ralph McConahy
      34.8829N  117.0064W  670m
      (viewed the ISS transit the sun from 34.8838N 117.0547W ~650m)
    
    
    
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