>From: Dean Norris, firstname.lastname@example.org
>At 06:53 1/7/97 -0800, you wrote:
>>"At the time (local) half way between local sunrise and local sunset,
>>the Sun, if shining, will cast a shadow exactly (true) North-South."
Actually, there's some variation in sunrise/sunset times. (ie the latest
sunrise and earliest sunset don't occur on Dec 21. Instead one occurs two
weeks before, the other two weeks after. Same thing for earliest sunrise
and latest sunset.) This is due to the fact that as the earth rotates, it
also moves around the sun. Since the orbit isn't exactly circular, the
speed of the orbit varies (hence, the sun appears to speed up/slow down
in its progress across the sky).
>>Just use the local weather forcaster's sunrise/sunset times and it's
>>accurate for amateur antenna alignment for sure!
Maybe not. The summer variation can be rather significant (a few
degrees). Best time for this is probably at or near the solstice or
>I live in a location where the takeoff angle to horizon to the east is
>virtually zero degrees, in other words, straight out. To the west the
>horizon is blocked by tall mountains and the takeoff angle is probably 20
>degrees. Will this make a difference to the sunrise and sunset times.?
Not if you use the local weather forecaster's times.
The better technique is probably the shortest shadow technique. The
objective is to determine which way the shadow is pointing at local noon.
(Although this is probably subject to sunrise/subset variation as well)
I think going to a pilot shop, looking at a chart and finding the nearest
isogonic line and then correcting your magnetic compass for magnetic
variation is probably the simpliest and most accurate.
Bill Coleman, AA4LR Mail: email@example.com
Quote: "Not in a thousand years will man ever fly!"
-- Wilbur Wright, 1901
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