[TowerTalk] And now for something completely different(TrueNorth)

Sun Aug 27 20:44:59 EDT 2006

At 04:34 PM 8/27/2006, Mike, K6BR wrote:

>Another good reason to use zip code calculator furnished by the government,
>see my previous posts. I cannot understand why people come up with so many
>complicated ways of doing something so simple.

Zip codes do have some problems.. the lat/lon in the database may not 
reflect where the actual mailing addresses are..

Example: Jet Propulsion Lab is 91109, and is at the far northwest corner of 
Pasadena on the border with LaCanada-Flintridge.  However, if you do a 
lat/lon lookup, it comes up with the position of the US Mail distribution 
center, which is 5 miles or so to the east. Granted, this is something like 
10-20 seconds worth of solar noon offset, but it's something to be aware of.

A bigger factor is the "equation of time", represented by that funky 
analemma on some maps and globes.  Depending on the time of year, solar 
transit occurs earlier or later than mean noon calculated from your 
longitude.  I assume the Naval Observatory website takes this into account. 
The cadastral one certainly does.

OTOH, if you align with when the sun is truly highest in the sky (as 
opposed to some modern new fangled approach like looking at a clock or 
watch), you will get pretty close to north.  The trick is knowing when the 
sun is highest, because it doesn't change very quickly. If you're using a 
surveyor's transit or sextant or similar optical instrument, you can do it, 
but having tried this with the "stick in the ground and marking on the 
dirt" approach, it's pretty darn tough.  For one thing, the sun is a half 
degree wide, so the shadow doesn't have all that sharp an edge.

If you want to use the Stonehenge era stick in the ground technique, you're 
much better off to measure two places where the sun is at the same 
elevation angle (say, around 10AM and 2PM, local solartime), and bisect 
it.  The elevation of the sun is changing a lot faster then, so it's easier 
to set the marks.

hey.. we argue about tenths of a dB here on the list.. why not argue about 
tenths of a degree in orientation.  If you're trying to outdo W6AM, and 
aligning your South London rhombic, you don't want to be pointing at some 
northern suburb instead, do you?

I think everyone should try and go do this, by several different 
means.  It's a nice picnic type project especially if there are kids 
around.  It's noticeably harder than it seems to get a real good measurement.

>Mike
>
>
>
> > Each time zone is 15 degrees wide [15 zones x24 hours =360 degrees]
>
>Theoretically 15 degrees wide.  I think you will be able to find some times
>zones that are over 20 degrees at their widest points.  The Eastern time
>zone in the US is a good example.  It runs from *about* 66 degrees in Main
>to over 86 in western lower Michigan.  "I think" the upper Peninsula is also
>
>eastern all the way to the West end. If it is all the way to the west end
>then it's 90W for a width of 24 degrees.  OTOH the boundaries are not any
>where near straight.
>
>At any rate whether the figures are correct or not time zone widths do vary
>considerably.
>
> > If some one lives at the 'edge' of one of those time zones, they can be
> > 7.5 [or more] degrees off the time zone meridian.  Therefore, at Noon
>
>As you emphasized the [or more] the meridian may not be centered.
>For instance the meridian for Eastern Time *should* be 75 degrees (a
>multiple of 15 degrees or one hour), but 75 degrees is very close to
>philadelphia with the western edge of lower Michigan being 86 degrees or 21
>degrees west of the meridian.  It'd be over an hour off for the sun being
>due south at noon. OTOH any one know what time zone Tennessee is in?
>
>
>Roger Halstead (K8RI and ARRL 40 year Life Member)
>N833R - World's oldest Debonair CD-2
>www.rogerhalstead.com
>
> > local time, they will NOT have the sun directly South/North [depending
> > on location relative to the Equator].  Only those who live EXACTLY on
> > the time zone meridian will!
> > The sun doesn't shift in 15 degree increments .. at least it doesn't do
> > that here!
> > Don
> > N8DE
> >
> >
> > Mike Murphy wrote:
> >> Don,
> >> What causes the error for one not living exactly on the time zone
> >> meridian?
> >>
> >> 73,
> >> Mike, WA4BPJ
> >> www.wa4bpj.com
> >>
>----------------------------------------------------------------------------
> >> -------------------------------------
> >> Here we go again.
> >> This method only works for those who live exactly on the time zone
> >> meridian.
> >> Don
> >> N8DE
> >>
> >> J A Ritter wrote:
> >>
> >>>Two sticks, one vertical, the other horizontal placed along the path
> >>>of the shadow at high noon will show True North...
> >>>
> >>>73,
> >>>Jack W0UCE
> >>>Website: www.w0uce.net
> >>>
> >>
> >>
> >> _______________________________________________
> >>
> >>
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