[illustratingshadows via sundial]

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a gnonom measures the hour angle of the sun around the earth north south polar axis. so it is set at latitude. you are correct.

the gnomon is parallel to the earth at the equator, and that is a polar dial, called so because the dial.plate parallels the polar north south axis. you were correct, except in concluding the dial would not work.

the gnomon at the poles is vertical, it's shadow falls on a dial plate paralleling the equator, and is thus called an equatorial dial, sometimes equinoctial dial. your observation was correct, your conclusion in error.

polar and equatorial dials can be used anywhere, with a dial plate tilt adjustment.

see my website

www.illustratingshadows.com 

or the NASS or BSS websites, or Carl's sundial primer site.

Simon W-S

Sent via the Samsung Galaxy Alpha™, an AT&T 4G LTE smartphone

-------- Original message --------
From: Phil Dorman <p...@wattagan.com>
Date: 11/15/2015 15:37 (GMT-07:00)
To: sundial@uni-koeln.de
Subject: Southern Hemisphere

Hi Everyone,

 

I joined this list because I have a specific question which I can’t find a definitive answer to.

 

I want to install a sundial at Perth WA Australia which is pretty close to 32deg South latitude.

From what I can determine that means the Gnomon should be 32deg above horizontal.

Or is that just for the Northern Hemisphere ??

 

As I move North in Australia the Latitude number gets Smaller

Eg Latitude of Brisbane QLD (further North) is 27.46deg

So presumably the Latitude at the Equator would be Zero !

Which would mean a sundial Gnomon at the Equator would be Horizontal ie Flat on the Ground

Which of course would not work.

And at the South Pole it would be Vertical 90deg from Horizontal and also would not work since there would be no ground for the shadow to fall on.

 

So. Am I correct to put it at 32deg from Horizontal for Perth WA or not ?

 

Phil Dorman /:~)>

Machinery Appreciation & Transport Engineering Society
946 Wattagan Crk Rd
Watagan NSW 2325

0419 501285

 

 

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