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[TowerTalk] Noon is NOT at 12:00, AKA Navigation 101

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Subject: [TowerTalk] Noon is NOT at 12:00, AKA Navigation 101
From: (
Date: Tue, 8 Jul 1997 01:47:29 -0400 (EDT)
Hi Gang,

too beat the dead horse a little more....

If you walk outside at 12 Noon and figure that is the sun is due south, it
may not be good enough for even alligning a dipole.

1. Time zones are based on standard meridians every 15 degrees.  The day is
24 hrs long.  The sun appears to us to make to make one revolution of 360
degrees, thus the sun "moves" 15 degrees per hour / 1 Degree every 4 minutes.
 My ship is presently in Galveston, TX which I'll use for the example.  Texas
is now on CDT so we are 5 hours from  Greenwich Mean Time.  This means that
we are actually keeping the "local" time of a place located at 75 degrees
west, like the Outer banks of NC.  Galveston, Tx, however is located at 95
degrees west longitude.  This means that if the sun was perfectly consistant
that local noon would occur in Galveston 80 minutes (4 minutes X 20 degrees)
later because we are west of our standard meridean, or 1320 local time.

2. The sun is not perfectly consistent.  Due to variations in the sun's
declination with the change of seasons, etc. Local noon varies as much as 17
minutes sooner or later than 12:00 at the standard meridean.  This is a slow
change like a sine curve through out the year.  This is called "the equation
of time".  Today, the equation of time is about 5 minutes (after noon).  We
add 5 minutes to 1320 local time and:

3. Meridian passage of the sun (azimuth of 180 degrees true) in Galveston, TX
today occurs at 1325 local time.

4. I punched the numbers into my calculator and figured the azimuth of the
sun at 12:00 local time today.  The azimuth is 105 degrees!!!!.....75 degrees


If you absolutely have to use the sun and don't have a nautical almanac or
don't understand spherical trigonometry, just use the "split the difference
between sunrise and sunset" method.  It will be close enough.

If you do know spherical trig, you can figure the azimuth of the sun at any
given time.   You can also use a GPS to do the spherical trig for you.  Every
GPS is a navigational calculator.

The easiest method is to just use Polaris (the north star).  It is ALWAYS
within 1 degree of true north.....Always (at least in our life times).  You
don't need a calculator, you don't need to find out your local magnetic
variation, or worry about compass error.....just a clear night, it's right
near the Big Dipper.  Stand back away from your tower and line Polaris up
with your tower.  Bang a stake in the ground.  It will be due south of your
tower.  It is real easy to align the antennaes with the stake from the top of
the tower.

Hopefully the horse has stopped kicking

73, Clint - W1LP/MM

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