[amsat-bb] Re: Sun shadow for True North
kl7uw at acsalaska.net
Fri Dec 28 18:47:10 PST 2007
For example Alaskan Standard time was politically moved ahead
(eastward) one time zone to be equal to Yukon Time and -1 hour from
Pacific (PST) Time. But solar noon was 13:06:39 this afternoon (when
the sun reached max elevation=6 degrees). I suggest one use NOVA or
many of the other tracking programs to find when the sun crosses your
local Meridian (i.e. is azimuth=180). Then the sun is exactly
south! I have used that to spot whether my eme antennas were off. I
could look at the tower shadow and align the antennas to be within a
few degrees. My Ham-IV rotator has about 10-degrees accumulative
error as I rotate clockwise 180 degrees. I had to make myself a
lookup table to keep on the Moon.
I installed an old TV camcorder on the antennas to visually track the
Moon, but it did not like the long video cable to the shack.
BTW we had 5:20:20 hours:min:sec of daylight today.
73 Ed - KL7UW
At 03:06 PM 12/28/2007, Tony Langdon wrote:
>At 05:29 AM 12/29/2007, Dave Guimont wrote:
> >A vertical rod about 4' long (plumb it, or use a level) will have the
> >shortest shadow at noon.
>Not necessarily. Ignoring DST, local solar noon can occur anywhere
>within a window of around 1 hour (give or take, depending on the
>exact borders of your local time zone), because each time zone is
>approximately 15 degrees wide (there are local variations that take
>the official zones beyond the 15 degree nominal zones). For example,
>here in Melbourne, local solar noon usually occurs around
>approximately 02:15 - 02:20 UTC (12:15 - 12:20 standard time or 13:15
>- 13:20 DST). In Brisbane, it occurs before noon AEST, despite both
>cities being in the same time zone. Using the "shortest shadow at
>noon" method, you can have an error of up to 10 degrees (now THAT
>would ruin the performance of your high gain antenna!). Here, it
>would be around 4-5 degrees, if one was ignorant of the actual time
>of solar noon.
>The moving shadow to find the East - West line is a much better and
>MUCH more accurate idea.
>73 de VK3JED
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Ed - KL7UW
BP40IQ 50-MHz - 10-GHz www.kl7uw.com
144-EME: FT-847, mgf-1801, 4x-xpol-20, 185w
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