Douglas Bateman <[EMAIL PROTECTED]> wrote:
I have a site on my browser, www.mapmaker.com/shadowfacts/sunweb.asp
that shows the terminator throughout the year. It is fascinating to
see how
rapidly the shape changes, ....
Already the sunclock shows the light is broadening in the northern
hemisphere.
Not even one full day into spring. Hmmm...
There was comment about the terminator being a great circle in actual
fact.
A Mercator projection shows lines of longitude parallel so the light
and dark
bands have straight lines between them at the equinoxes.
But is the terminator really a great circle and can we tell the
difference on the
sun clock? The sun is not infinitely far away and on that account less
than half
the globe would be illuminated. However, the sun's disk subtends ~1/2
degree
at the earth which would make more than half the globe illuminated.
Finally, due to refraction by the curved atmosphere, we see some piece
of
the sun's disk before said piece is over the horizon.
My question: what is the sum of these effects (and any I have
forgotten)?
What fraction of the earth's surface can see some part of the sun's
disk at
any given time?
Thanks,
John
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