|
Hi
all,
I have
a trick for remembering the approximate
details of sunset and refraction. I like to run
it
by all
of you for review. Hopefully my sketch
appears below.
I
imagine I'm on the equator at equinox and the sun
is
setting due west, straight down. Then, first
ignoring refraction, the common sense sunset is
obviously one solar radius after the theoretical
center
point or approx. one minute later. Now
add
refraction to the image by simply moving the
sun
down one more diameter (approx).
Therefore at sunset I see the sun just below the
horizon and know that the actual sun is one more
tangent diameter lower...two balls hanging below
the
horizon. Therefore sunset appears 1-1/2 dia,
or 3
minutes after theoretical, uncorrected
centerline sunset.
Now to
correct this image for your latitude, tilt your
head
equal to your latitude. The time delays are
stretched by dividing by the cos of attitude.
This
is 20%
for me at 33 N.
This
means that here at 33N on equinoxes, west is
actually .4 degree (little less than solar dia) south
of
the apparent refracted disappearing solar limb.
This
is from = 3/4 degree (1-1/2 suns) times sin
lat.
Fritz Stumpges |
