ISS Transit prediction problems?

From: Thomas Fly (
Date: Sun Aug 31 2003 - 00:33:38 EDT

  • Next message: Kevin Fetter: "Re: ISS Transit prediction problems?"

    Hi Willie,
    Somebody else (from the UK) had a similar complaint- he was using "The Starry
    Night Backyard."  I checked with CalSKY, however, which confirmed the
    prediction.  I also checked this prediction with CalSKY, and again it confirms
    the transit- see the attached CalSKY HTML file.
    The point about the azimuth being wrong seems to be valid- that's what you get
    for not living in the Northern hemisphere!  (Maybe it should be 123 degrees west
    from south?)
    By chance, I observed my first ISS solar transit today!!! It was touch & go, as
    big clouds gobbled up the sun twice, while I was setting up. I'd taken along an
    ancient Radio Shack "Time Cube" (that receives the U.S. government atomic time
    broadcasts), as my cue to click my Kodak DC290 in 2 fps burst mode, only to
    realize that the road I was parked along went to a local water treatment plant,
    and had a high-voltage power line that drowned out WWV for 100 feet to either
    side!  I projected a 5" diameter image of the sun onto a slide projector screen,
    which gusts of wind conveniently knocked into my camera tripod & telescope a
    couple times...
    At some point, I stuck my head inside the car to read (after my pupils had
    dilated enough) that it was now 1:06 PM (transit predicted at 1:07:00), and as I
    got back, I thought I saw a speck go across the sun... but a few seconds later,
    an upside-down T went zipping across, startling me for a number of reasons,
    including how large it appeared to be!
    While I was on my predicted (roughly 48 hours in advance) centerline- - the transit was about 1/4
    of a solar radius to the southwest, implying that the centerline actually was
    about 0.3 miles to the southwest.  Curiously, yesterday evening CalSKY had
    indicated that the centerline was about 0.25 miles northeast of my prediction.
    (Roland Stalder used CalSKY to fine-tune his aiming, which was exceptionally
    well-centered, despite the relatively small field-of-view of his movie... just
    good luck?)
    You can sign up for ISS fly-over alerts (either "all" or "visible only") at
    You can also make use of
    ml  When I enter 33.9375 S, 18.4736 E, it indicates a "solar separation" of 0.3
    degrees at 16:00:40 (and an azimuth of 303 degrees east from north, which would
    be 123 degrees west from south :)
    When I click on "SkyTrack," it gives me a "NASA SkyWatch" applet that shows the
    ISS nailing the sun, while Venus looks on.
    And after all of that, I believe I see your problem- the times given are your
    local time, not UT!
    ----- Original Message -----
    From: "Willie Koorts"
    To: "ISS Transit" <>
    Cc: "Greg Roberts"
    Sent: Saturday, August 30, 2003 10:26 AM
    Subject: ISS Transit prediction problems
    Hi Tom
    Thanks for the regular alerts.  Unfortunately, I have not had the
    opportunity to try any since they happened almost always on inconvenient
    times for me.
    The last one you sent again is due in Cape Town while I'm doing standby
    duty at our observatory outstation in Sutherland.  I sent the data to a
    friend who found some problems with your predictions.
    Attached are his findings.  Could you please investigate?
    ---------- Forwarded message ----------
    Date: Sat, 30 Aug 2003 08:20:43 +0200
    From: Greg Roberts
    To: Willie Koorts
    Subject: Fw: ISS Solar transit
    I checked the ISS transit alert- something is wrong-- if time is 16hr UT the
    sun cant have an azimuth of 123 degrees - it must be 360-123= 237 and even
    that doesn't look right as I don't think the suns that far south I
    reading the prediction wrong - see its for Monday 1st Sept.
    ---------- Forwarded message ----------
    Date: Sat, 30 Aug 2003 10:10:21 +0200
    From: Greg Roberts
    To: Willie Koorts
    Subject: Re: Fw: ISS Solar transit
    I've done a check with GUIDE - and element set dated Aug 29. ISS is nowhere
    near the sun- in fact well below the horizon. The position of the sun at
    16h00m38s UT is azimuth 283.18 deg, elevation 4.65 degrees so something
    wrong somewhere - hope I haven't made a mistake but it definitely looks like
    the prediction supplied is garbage :-))
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