geo flare calculator by Jeff Umbarger

From: Kevin Fetter (
Date: Tue Feb 27 2007 - 21:11:36 EST

  • Next message: Greg Roberts: "Optical 27 Feb 2007"

    Jeff has aked me to post this, since I am storing his files on my website.
    Hey All,
         It's that time of year again, the beginning of
    the 2007 Vernal Equinox Geosynchronous
    Satellite(geosat) Flare season. And thanks to Kevin
    Fetter, I've posted a series of GIF image files of the
    celestial star field where all of this will be
    occurring so we all have a chance to see this. There
    is also an Excel spreadsheet that has all my equations
    and tables that I used to generate this. The main
    image located at:
    I would suggest that you print this email and image
    out and use it to follow the instructions below. The
    80KB spreadsheet is located at:  
    Flaring Geosats
         This is when the sun, as it slides up the
    ecliptic and approaches celestial equator (vernal
    equinox), illuminates the reflective surfaces and
    solar array panels on all the geosats on the night
    side of the earth and this light is returned to the
    earth's surface on the night side. This can be quite
    spectacular when viewed from below at night as "stars"
    appear to form and then disappear all night long, in a
    very thin line stretching east and west near the
    celestial equator. Over the period of a night it looks
    like someone is slowly sweeping a flashlight along a
    string of diamonds. These are the brightest, "flaring"
    geosats. They will rival some of the brightest stars
    in the sky. And if you have a telescope or binoculars,
    you can see many more geosats. They will appear as a
    ghostly train of lights silently marching in a line
    across the star field. At 36,000 km or nearly 5 earth
    radii away, these are the most distant manmade objects
    you will ever see. 
         Where you look depends on your latitude and the
    date. Because of parallax, the geosat orbit and all of
    its many satellites will appear at a specific
    celestial declination depending on your latitude. For
    instance at my latitude, +33N, all the flaring geosats
    will appear along the -5 degree declination. Also the
    best date for my latitude this season is March 7 (at 0
    UT). On the diagram, which has North up and and West
    to the right, there are a series of red and green dots
    streching from the upper left to the lower right and
    there is a red dot for me labeled "7 Mar: +34D" and
    the dot lies on the -5 declination line. However, this
    isn't the only date I can go outside and see flaring
    geosats. If I choose other nights, I will still always
    look along the -5 degree declination. The section of
    the -5 degree declination I look at will be the
    section directly below or above (depending on the
    date) the anti-solar point –the point in the sky
    exactly opposite the sun. It is not shown on my image
    but it rides down the ecliptic night after night. The
    ecliptic is the black line going from the upper right
    of the image to the lower left. This is where the
    earth's circular shadow is near. In fact, the earth's
    shadow begins to cover more and more of the geosat
    orbit below the anti-solar point as the vernal
    equinox is approached. The green dots to the left
    (east) and right (west) of each red dot define the
    chord length of the earth's shadow on the red dot's
    date. This reaches a maximum on March 21 (0 UT) when sun
    crosses the celestial equator and shadows or
    "eclipses" nearly 20 degrees of the geosat orbit as
    viewed from our equator. It is important to know where
    the eclipse segment of the geosat orbit is because as
    all geosats enter this segment from west to east they
    will disappear before emerging on the east side. *And
    it is usually at these entry and exit points of the
    shadow that geometry is optimal for a geosat to
    Using the Graphical Calculator
         To use the graphical calculator, open up the
    above image file in a browser or image processing
    application. Then read the labels of the *red* dots
    from the lower right to the upper left. Each has a
    date and an earth-based latitude associated with it.
    For instance, with me living at the +33N latitude, I
    would use the red dot associated with the label "7
    Mar: +34D" near the lower right of the image, since the
    +34N latitude is closest to me. The date, "Mar 7" is
    the date that flaring should be optimal for me. At the
    same declination as each of the red dots in the chart
    are two *green* dots of equal distance to the east and
    the west. These two dots represent the eclipse entry
    (the right or west green dot) and the eclipse exit
    (the left or east green dot) of a geosat. *You must be
    certain to only use the two green dots EXACTLY on the
    same declination as the red dot.* This is hard to do
    and may require a ruler to get the right set of green
         So here is the procedure for using the geosat
    flare graphical calculator on the optimum date for
    your latitude, and then, on all other non-optimal
    1.) Print out the calculator:
    2.) With a ruler and a pencil, draw a line - exactly
    parallel with the celestial equator - across the
    entire image through the red dot and the two green
    dots associated with your optimal date and latitude.
    (Be careful not to draw the line over any stars since
    you may want to use these stars at night as guides and don't
    want them covered up in your image.) An example of
    where I have done this for my optimum date (Mar 7) and
    latitude (+33N) is shown here:
    In the image, as the night of Mar 7 progresses for me
    at +33N latitude, geosats will drift from right (west)
    to left (east) down the red line. As the geosats
    approach the right green dot, they will brighten,
    perhaps to unaided visible eye brightness (flare).
    Then, as the geosats pass the right green dot, they
    will disappear into the earth's shadow, only to
    re-appear at the left green dot later in the night. 
    From here they will continue to drift east along the 
    red line and dim significantly.
    3.) Most importantly, if I want to go out on any
    "non-optimal" night, I can use the calculator on those
    nights as well. Let's say, for my latitude at +33N, I
    want to go out on the night of March 19. First I
    would use a chart that I had already drawn my optimal
    declination line (v2007_02.gif, above). Then I would
    draw a similar line through the Mar 19th red dot
    and green dots. Then I would draw two vertical lines 
    down from the green dots on March 19 to my optimal 
    declination line for +33N. See here:
    Again, just like in the Mar 7 example, the geosats
    will drift right to left down the red line and
    disappear at the west green line and then re-appear at
    the east the green line.
    Other Times to Observe Geosat Flares
         This calculator is designed to be used at "local
    midnight", a point in time at night half way between
    sunset and sunrise (not necessarily 12:00am). At this
    point the red dot is exactly halfway between the two green
    dots at it's declination. However, as Ed Cannon and
    others have seen, a great time to observe geosat
    flares is at sunset and sunrise. At sunset, you would
    look at the eastern horizon and see that the two green
    dots are shifted such that red dot and the *right*
    green dot occupy the same spot and the left green dot
    has not risen above the horizon yet. Since this shows
    that optimal geosat flare position (red dot) is so
    close to the edge of the earth's shadow (green dot),
    you will have a much better chance of seeing a geosat
    IMPORTANT NOTE: This is unproven technology! I have
    confidence in where the red dots go, but less
    confidence in where the green dots go. I would be
    interested in any observers seeing flaring occurring
    *between* the green dots. 
         I would be interested in any feedback or
    questions that anyone has on the directions or
    usefulness of this graphical calculator. Please send
    those questions back to me directly. And please let me
    know if you have been successful as well. Enjoy this
    year's Geosat Flare Season!
              Jeff Umbarger
                   Plano, TX USA
                   Lat: -96.76802W
                   Lon: +33.0696N
                   CST (GMT-6)
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