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Re: Beam Headings for the Birds

Right.  Here's another KISS answer.

Draw a straight line from you to any satellite within view.

Now find the point on the Earth directly below the satellite and plot that point
on a map of the Earth.

Draw a line on the map of the Earth from you to that point on the Earth directly
below the satellite.

Your straight line to the satellite is now projected onto the map of the Earth
as a great circle route.

The azimuth to the satellite is the same azimuth to the point below the
satellite.  Which is why in a tracking program, the shortest distance to that
point below the satellite is in the same direction as the satellite.

>  > circle route from my location (Chicago), yet drawing on a map, west is not
>  > in a straight line to the bird.

What kind of map projection are you using?  The line could be straight or
curved, depending on the map projection.  On a rectangular projection, like what
most tracking programs use, a great circle route is not always a straight line.


----- Original Message -----
From: Tate <73KC7ZRU73@cyberhighway.net>
To: <amsat-bb@AMSAT.Org>
Sent: Tuesday, January 18, 2000 23:44
Subject: Re: [amsat-bb] Beam Headings for the Birds

> This may be an over application of KISS - but here goes:
> Terrestrial great circle paths exist because the earth is a sphere (at least
> close enough for this thought model)
> A satellite in orbit about this earthly sphere is also moving along the
> of another sphere - it's orbit.
> Great circle still applies.
> Only difference would be the relative angles dictated by connecting the
> shortest possible line from a point on the surface of the smaller sphere to a
> point on the larger sphere (without re-intersecting the surface of the smaller
> sphere - unless you're working some of the unusual propagation we've been
> hearing about).
> So I'd say, yes - great circle thinking applies - mostly
> Ok gurus - close enough?
> 73

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