[Antennas] Using GeoClock To Find True North

Mon, 18 Feb 2002 19:44:48 -0500

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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> 
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