[Antennas] Using GeoClock To Find True North

Mon, 18 Feb 2002 19:25:13 -0600

This was written up in"Ripley's Believe It or Not 18th Anniversary Edition"
if I recall.  It seems to me that they indicated that you were supposed
orient the stick for "no shadow" (pointed directly at the sun).  Also, the
length of the shadow entered into it as well.  I'll try to run that down.

 ----- Original Message -----
From: "Don Havlicek" <[email protected]>
To: "Jim Clark" <[email protected]>
Cc: <[email protected]>
Sent: Monday, February 18, 2002 6:44 PM
Subject: Re: [Antennas] Using GeoClock To Find True North

> Remarks inserted below:
>
> Jim Clark wrote:
> >
> > As the azimuth and elevation of the sun increase from sunrise to noon
> > and decrease from noon to sunset a plot of the shadow will describe a
> > straight segment from west to east of which the perpendicular bisector
> > will be north/south. Try it!
>
> The only way this would occur would be IF:  you were at the Equator and
> the day was either the Vernal or Autumnal Equinox [when the sun is
> directly over the Equator.
> The TIP of the shadow, on ANY day of the year in North America,
> describes an ARC [very nearly elliptical] from 'near West' to 'near
> East', with the maximum 'north' position being at TRUE Solar Noon.
>
> > To do what you describe the sun would have to be at the same elevation
> > all day and then you would be at the North Pole in summer or South Pole
> > in winter.
>
> At either pole, the sun is only at the same elevation above the horizon
> for ONE day, namely the first day of the LOCAL Summer.
>
> Don - N8DE
>
> >
> > Jim, N5QL
> >
> > -----Original Message-----
> > From: [email protected]
> > [mailto:[email protected]] On Behalf Of Don Havlicek
> > Sent: Monday, February 18, 2002 5:41 PM
> > To: Jim Clark; [email protected]
> > Subject: Re: [Antennas] Using GeoClock To Find True North
> >
> > As the sun rises, the tip of the shadow will move from near West to a
> > point approaching North .. then, after Noon, it will approach East.
> > Therefore, the segment from 0900 'tip' to 1000 'tip' will be somewhere
> > along a SW/NE line.  Sooooo .. the permendicular bisector of that
> > segment will be close to NW/SE !
> > Don
> > N8DE
> >
> > Jim Clark wrote:
> > >
> > > Just a thought
> > > As the sun "rises" between 9 and 10, the 10 o'clock shadow will be
> > lower
> > > and back in the E/W plane, maybe?
> > >
> > > Jim, N5QL
> > >
> > > -----Original Message-----
> > > From: Don Havlicek [mailto:[email protected]]
> > > Sent: Monday, February 18, 2002 5:17 PM
> > > To: Jim Clark
> > > Cc: [email protected]
> > > Subject: Re: [Antennas] Using GeoClock To Find True North
> > >
> > > No, no, no .... if the two marks were made at 0900 and 1000, then N/S
> > > line would be somewhere close to NW/SE !!!!!
> > >
> > > Better to do this:
> > > 1.  Drive the stick into the ground and mark the end of its shadow at
> > > some time in the early morning, recording the clocktime.
> > > 2.  Mark the the end of its shadow again at a time which is the SAME
> > > AMOUNT AFTER noon that the first mark is BEFORE noon.
> > > 3.  Now do what you suggest:  the perpendicular bisector of the
> > segment
> > > between the two points is APPROXIMATELY the N/S line.
> > > 4.  Better way:  Use the North Star as someone previously mentioned.
> > > 5.  Best way:  Use a compass and apply the correct declination
> > > correction.
> > > Don
> > > N8DE
> > >
> > > Jim Clark wrote:
> > > >
> > > > This sounds like a job for Indiana Jones or Laura Croft. (I'll take
> > > > Laura!)
> > > >
> > > > Egyptian compass:
> > > >
> > > > Pick a nice sunny day.
> > > > Drive a stick several feet long into the ground straight up.
> > > > Mark the end of its shadow with a small stick.
> > > >
> > > > About an hour or so later mark the shadow's position again.
> > > > Draw a line between these two points.
> > > > A line perpendicular to that line is north / south.
> > > >
> > > > Jim, N5QL
> > > >
> > > >
> > > >
> > > > - - -
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