dxAce wrote in message ...
bpnjensen wrote:

dxAce wrote in message ...
bpnjensen wrote:

dxAce wrote in message ...

snips

No, the grey line is not always necessarily a straight line path, but can be a
'crooked path', and that is 'veering around corners' as you say.

Hmmm - can you explain this?

Geometrically, with the sun's rays essentially parallel to one another
shining on the disc of the earth, the grayline would always represent
a virtually perfect circumference, no matter which exact face the
earth presents to the sun - hence, while a flat map of the world shows
an undulating wave, the grayline is actually a 'straight' line along
the earth's face. The only deviation from this that I can determine
would be the astronomical width of the sun, about 0.5 degree, and
whatever 'ionic' width either side of that partial illumination at
sunrise/sunset would be involved in improved propagation.

I can imagine that something about the earth's magnetic field could
vary this, especilly *at* the poles - is this why some 'crookedness'
can occur?

It's very easy to see, just look at a grey line map.

It's a well known propagation phenomenon.

At least amongst the cognoscenti.

And, has nothing to do with the magnetic field.

dxAce
Michigan
USA

A "map" is not an accurate representation of the globe's surface - if
it is not on a spherical surface, then every single object plotted on
a map has some degree of distortion. The lovely sine-wave shaped
grayline you see on a typical flat map is a distortion of its true
shape, just as the map itself is a distortion of the earth's surface.

In reality, a grayline is a virtually perfect circle in a single plane
slicing through the center of the planet, corresponding to the
terminator of the sun's rays as they reach the earth. Even the
grayline websites admit this.

It is fairly easy to visualize. Put a ball (the earth) up in front of
you, with a bright small light (the sun) situated about 15 feet away.
Look at the side of the ball - the gray area at the horizon traces a
neat planar circle around the perimeter of the ball. Same with ol'
sol and terra, except on a bigger scale.

That, from a cognoscentus of simple geometry and astronomy.

Bruce Jensen