Re: Vertical stereographic sundial

[Peter Mayer]

Hi Maciej,

Here's a puzzle for you and others on the list. Does the usual 
'co-latitude' rule for other plane sundials hold for 
Oughtred/stereograph dials? I've tried a quick empirical experiment 
using _Orologi Solari_ creating a vertical stereograph for my latitude 
(35S) and a horizontal for the co-latitude (55N). The two seem identical 
(except for the numbering of hours). It's not a 'geometric proof' but it 
seems entirely reasonable.


I had meant to add in my earlier post that a few years ago I, too, wrote 
a DeltaCad macro for an Oughtred dial. Unlike the elegant trigonometry 
used by Valentin, I tried to replicate the protractor, compass and 
straightedge methods in a traditional construction. Once it worked for 
my Southern Hemisphere location, I stopped working on it, so it is 
really a beta version, but I'm happy to forward it to anyone who is 
interested.


best wishes,

Peter

On 2/11/2022 5:25:29, ml...@interia.pl wrote:

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Hi Peter,

Thank You for the links.

My plea concerned vertical stereographic sundials - not the horizontal 
ones. I'm aware that there are a number of programs to construct 
horizontal sterographic dials.


Helmut Sonderegger kindly proposed to include vertical ones in Sonne, 
when he finds a time for it, and the info form Valentin was that for 
the vertical plane he actually worked on a spider dial, which is most 
interesting but of different type than stereographic.


But I must admit that I was unaware of construction possibilty of 
vertical stereographic dials (under the name "vertical astrolabe") in 
Oroligi Solari.


Though, the program doesn't give any limits for the gnomon - which in 
this type of instruments is no longer that 1/2 the dial's radius, as 
discussed in my paper, irrespective of walls' declination, latitude 
and sundial's plane inclination. It doesn't also give options for 
inclining dials. So there is some space for it to be upgraded making 
this very nice typology more approachable for sundial makers. Also, 
derivatives like the four-sided, "gnomon-less" stereographic vertical 
sundial could be included.


Drawing by hand (with CAD) is obviously time consuming, but it allows 
for understanding of geometrical relations behind and allows for 
inclusion of elements not available in the custom software. So not 
being a skilful programmer, I will rather stay with that ! But for the 
sundial makers it is obviously easier to use a software.


Regards,

Maciej


Od: "Peter Mayer" 
Do: sundial@uni-koeln.de; ml...@interia.pl;
Wysłane: 5:58 Poniedziałek 2022-10-31
Temat: Re: Vertical stereographic sundial

Hi Maciej,

Thanks for your recent post. Since no one seems to have replied to
your plea in the final paragraph for software to draw a
stereographic/Oughtred dial, here are some existing open software
options:

* Gian Casalegna's _Orologi Solari_ will draw one: azimuth:
horizontal/vertical: astrolabe

*Helmut Sondereggers' Sonne will draw at least a horizontal
stereograph: Azimuthal: Sun Altitude

* Valentin Hristov has written some elegant code for DeltaCad
:www.math.bas.bg/complan/valhrist/az-ht.bas

[When I tried to re-run it a few minutes ago, it now seems to be
stuck in a loop which I haven't had time to debug. I've attached
an example which I created about 4 years ago].

So: no need to create a stereograph by hand!

best wishes,

Peter


On 27/10/2022 4:02:34, ml...@interia.pl wrote:

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Dear All,

As proven in a separate tread on "Sun elevation tool/
horizontoscope", stereographic projection is
a fascinating geometric construction with great potential in
gnomonics.

During last year I explored the idea of vertical stereographic
sundial and it resulted in
a paper describing several stereographic sundial types:

- vertical stereographic sundial, for walls of any declination
and for any latitude,
- four-sided stereographic vertical sundial, attractive for its
“gnomon-less” form,
- double – stereographic & polar – vertical sundial for walls of
any declination, a vertical reference to Oughtred’s horizontal
design,
- folded pocket, double stereographic & polar – vertical sundial
- inclined, proclined and polyhedral stereographic sundials

The paper can be downloaded free of charge from Cursiva
publishers website:


http://cursiva.pl/e-ksiegarnia/vertical-stereographic-sundial-properties-construction-and-related-instruments/



or from Academia.edu website:

Re: Metal gnomons

[Michael Ossipoff]

What’s wrong with brass changing its color with weathering? Isn’t that part
of the appeal of brass?

On Sat, Apr 30, 2022 at 8:56 AM Dan-George Uza 
wrote:

> Hi,
>
> Iron rusts and brass changes color, but what about different metals used
> as gnomons, pros & cons?
>
> What would be the appropriate choice of material for a replica of an 18th
> century cubical multiple sundial? It should ideally come as an industrial
> sheet ready for cutting and also not stain the limestone face.
>
> I like the metal in the attached photo (Sundial Atlas CH 000247). Do you
> know what it is?
>
> Thanks,
>
> Dan Uza
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
>
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Norths align in the UK

[Dan-George Uza]

Hello,

This is interesting:
https://www.ordnancesurvey.co.uk/newsroom/blog/magnetic-true-grid-north-align-over-great-britain

Cheers,

-- 
Dan-George Uza
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