RE: Seasonal Sunrise Marker

[Roger Bailey]

Hello Anselmo,

The times of sunrise and sunset can be easily determined on a vertical
declining dial that has declination lines. The horizontal line from the base
of the gnomon is the horizon line. The intersection of the declination line
and the horizon line shows the time of sunrise or set. This is of limited
use on south facing dials as the scale of the gnomon and resulting
declination lines is usually to great to show much more than the winter
solstice. Declining dials, east  for sunrise and west for sunset show the
times  well. You also get a sense of the azimuth as this is the line from
the intersection point through the tip of the gnomon to the distant horizon.
This may seem obvious but it is not. The vertical declining dial on my house
shows hour lines above the horizon line. I did not realize the problem until
I checked the design using Fir's program. It clearly showed the horizon line
and sunset times.

I do not know if this answers your question. It addresses sunrise and sunset
times but does not look at insolation times, how long the sun is on the
dial.

Roger Bailey
Walking Shadow Designs
N 51  W 115

-Original Message-
From: [EMAIL PROTECTED]
[mailto:[EMAIL PROTECTED] Behalf Of Anselmo Pérez
Serrada
Sent: January 12, 2002 3:56 PM
To: Sundial, Mailinglist; fer j. de vries
Subject: Re: Seasonal Sunrise Marker


Fer,

I have read in Rafael Soler Gaya's book that you can
rotate these circles (or the approximation by straight lines) you have drawn
so that
they can tell you as well the sunrise and sunset hours for any vertical
declining dial...
The problem he says that incidentally in a very brief paragraph and perhaps
I
misunderstood his words. Do you know if that is true?

Cheers,


Anselmo

A sundial trade catalogue

[peter ransom]

I've just acquired a very nice piece of dialling ephemera. It is a trade 
catalogue, 8 inches by 5 inches high, entitled "Where SunDials are Made".


It describes, with illustrations, text and in some cases prices, of sundials 
(vertical, annalematic (yes, spelt that way), combination (horizontal and 
annalematic), universal) and pedestals available from E.B.Meyrowitz, 
optician of New York (3 addresses), St. Paul, Minneapolis and Paris. There 
are 13 interior pages with illustrations and text, and a nice illustrated 
cover. The only indications of date are 1902 on the vertical sundial and 
"Copyright 1908 by E.B. Meyrowitz" on the back cover.


I'm happy to photocopy this and send a copy to anyone who sends me £2, 5 
Euros, or $5 cash (sorry - I don't want to pay the horrendous bank charges 
on small cheques) to cover the cost of copying and postage and packing.


Peter Ransom
29, Rufus Close
Rownhams
Southampton
SO16 8LR
UK


_
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On conical gnomon sundials and anti-vandalic designs

[Anselmo P�rez Serrada]

Edley,
 
You can see one of these conical gnomon sundials in 
the web page of the city of Gent in Belgium.
This is a clever and elegant design, and very 
easy to put into practice.
 
Another of its virtues is that these dials are 
more robust, ie., VANDALS-PROOF, than ordinary ones.
This is a property which, at least here in Spain, is an 
essential one (!). I know there are more dials with
that kind of 'robusness' (for instance, several 
polyhedrons laid so that one casts its shadow over the other),
but does anybody know about some more dials like 
these?
 
Anselmo

  - Original Message - 
  From: 
  Edley 
  McKnight 
  To: Steve Lelievre 
  Cc: fer j. de vries ; sundial@rrz.uni-koeln.de ; Warren Thom 
  
  Sent: Sunday, January 13, 2002 9:57 
  AM
  Subject: Re: Acadian domestic 
  sundials
  Hi Steve, Fer, Warren, Dialists 
  all,I'm remembering more and more regarding notch dials that tell the 
  number of hours til sunset.With what I've been reading lately of all 
  the richness in the NASS repository CD, much of what I was told, but didn't 
  understand at the time is making a great deal more sense.I'll explain 
  the basic procedure of what I've been told as the main ideas and then expand 
  on them.I was told in other terms, but it seems to be easier to relate 
  to an article written in 1998 by Javier 
  Moreno Bores in the NASS Compendium of June of that year called "A NEW FAMILY OF SUNDIALS WITH CONICAL 
  GNOMON". In that article he covers a number of dials giving Italian and 
  Babylonian hours using cones as the gnomons. The particular dial of interest 
  is the horizontal dial.As he explains this:1. First create a 
  standard horizontal dial for the latitude with half hour lines.2. Create a 
  cone with an included angle of twice the latitude.3. Place the cone in 
  place of the gnomon on the horizontal dial with the point of the cone pointing 
  due south touching the point all the lines come together and the cone axis 
  then parallel with the earth's axis and in contact with the substyle 
  area.4. Each half hour line extending to the west of the cone is where the 
  cone's shadow will mark the hours before sunset starting from close to the 
  cone and moving outward.Now, take a flat thin blade and place it in 
  contact with the cone and the sharp edge in contact with the line of a given 
  hour before sunset and apply pressure along the plane of the knife forcing it 
  into the surface some considerable distance and rock it slightly to open a 
  kerf or deep narrow notch which now, when the sun's light fills it fully 
  indicates that hour before sunset. If the surface was of limited depth the 
  knife could be forced all the way through leaving a thin slit. If all the 
  hours were so made into slits then if this board were lifted up a bit the 
  light would shine all the way through and make a lines of light on a surface 
  below which would indicate, again, the hours before sunset. This board could 
  be used as a template to mark the lines on another surface.Now, 
  starting with a fresh surface, If one slowly brought the knife to the proper 
  angles for say each of the six hours before sunset as it was drawn along the 
  cone we would have a long curving line with the angle of the kerf varying as 
  the angle on the surface changed. If this were done slowly enough the one line 
  would be able to tell all the times in the interval from 6 hours before sunset 
  to sunset. If one were a master wood carver then one could even remember that 
  cut and be able to make it whenever and wherever we wanted. With skill the 
  hours could be made to be linearly spaced along this curve and so 
  marked.An exact mirror curve could be cut on the other side of the 
  cone and thus mark all the Babylonian hours or hours after 
  sunrise.This sounds like a pretty nice sundial, I'll try making it 
  myself.Apparently this approach will work well only in the middle 
  latitudes from say 20 to 66 degrees.I hope this sounds like as much 
  fun as it does to me ( after a mostly sleepless night thinking about it. 
  )Good luck in your search, I hope this is what you are looking 
  for.Edley

Re: Seasonal Sunrise Marker

[Anselmo P�rez Serrada]

Fer,

> I have a book by Rafael Solaer, printed in 1989 but I can't find anything
> about the Lambert's Circles.
> So I can't answer your question because I don't know what was meant.

Oh, it's in the second edition (1996), page 401 but, never mind what he
says there, because the problem still stands: is it possible to modify your
construction (or maybe the approximate one) so that it shows the insolation
hours for *any* vertical flat dial ? And if not, is there any other way to
show that?
I guess there must be, but I can't see the way.

Anselmo

Re: Caustic and 2 minute limit.

[Patrick Powers]

Message text written by INTERNET:[EMAIL PROTECTED]

> Since a caustic is a very different animal from an image, is there any
chance of getting around the 2 minute limit on sundial accuracy due to the
 sun's angular diameter?  <


I don't think anyone has yet come back on the specific point made by Art on
use of the caustic and I was very interested in its possible use as a means
to obtain greater accuracy in sundialing applications.

I cannot pretend to be a mathematician - just an engineer - but it seems to
me that the appeal of the cusp idea comes from:

1.  The cusp of the caustic is actually formed from those rays that are
nearest to and parallel to the axis.  Other rays parallel to the axis but
which are increasingly off-axis are directed increasingly more toward the
mirror that those nearer to the axis.  This is what forms the caustic.

2.  Slightly divergent rays arriving at the mirror at the same point as
some that are parallel to the axis will be directed nearer to the cusp that
those parallel to the axis so perhaps providing an element of compensation
(or focusing) for such penumbral rays.

The contra-indications are:

1. In any spherical (or cylindrical) reflexions the cusp so produced is
situated at a point mid way between the centre of the reflecting circle and
the pole of the mirror making the whole dial twice the physical size

2.  From experiment, the width of the cusp is approx 0.6mm across for a
mirror of some 125mm in diameter.  

3.  If we consider an equatorial dial design with (say) a 125mm diam
cylindrical mirror surface positioned around a circular frosted glass
plate; the whole in line with the ecliptic:

Radius of mirror equals 62.5mm
Radius of time scale on which the cusp 'sits' is (0.5 x 62.5) = 31.25mm
Arc length of semicircular time scale available to accommodate 6 hours (720
mins) is PI*31.25 = 98.17mm


If we assume that one can just discern a shift of a quarter of the spot
size this would permit a theoretical time precision of: 720*0.15/98.17 =
1.1mins.

I suspect, though do not know, that the width of the cusp will be roughly
proportional to mirror diameter so maintaining this approximate
relationship.  If so we shall probably not be able to use a reflected cusp
to obtain a significant improvement on the precision with which we may read
dial time.

However, I guess we probably knew that from the 'free lunch' argument!

Patrick

RE: Equatorial Ceilng Dial

[Ian Maddocks]

Hi John,

-Original Message-
Let's say you have a spherical room, built like a planetarium, where the
walls curve up into the ceiling and you locate your mirror in the
center.
(Actually, the room would be a quarter sphere, like an orange segment,
with
one flat side being the floor, and the other flat side the southern wall
with the window with mirror).
Would the sunspot be perfectly round all the time?  Also, what would the
hour and declination lines look like? (Like the lines on a
hemispherium?)
Would this be called an "Equatorial Ceiling Sundial"?
- Original Message -

I believe what you're describing is rather like the Helios XXII
sculpture by Barry Mason, except he uses a pond rather than a mirror to
much more dramatic effect.
See  http://www.rbs.org.uk/cgi-bin/getMember.cgi?member=083
Barry gave a talk on his sun sculptures at the 2000 BSS annual meeting
2000.

Regards

Ian Maddocks

Equatorial Ceilng Dial

[John Carmichael]

Hi Fer & others:

Let's say you have a spherical room, built like a planetarium, where the
walls curve up into the ceiling and you locate your mirror in the center.
(Actually, the room would be a quarter sphere, like an orange segment, with
one flat side being the floor, and the other flat side the southern wall
with the window with mirror).

Would the sunspot be perfectly round all the time?  Also, what would the
hour and declination lines look like? (Like the lines on a hemispherium?)
Would this be called an "Equatorial Ceiling Sundial"?

John

John L. Carmichael Jr.
Sundial Sculptures
925 E. Foothills Dr.
Tucson Arizona 85718
USA

Tel: 520-696-1709
Email: [EMAIL PROTECTED]
Website: 
- Original Message -
From: "fer j. de vries" <[EMAIL PROTECTED]>
To: "sundial" 
Sent: Friday, January 11, 2002 7:19 AM
Subject: Polar Ceing Dial


> Diallists,
>
> In my message of 2002-01-09 about the limits of a polar dial on a ceiling
I
> ended with:
>
> < Who has an inclined ceiling, higher at the south end?
> < Won't that be better?
>
> I wanted to know this for sure and I started with a ceiling with an
> inclination of 160 degrees in stead of 180 degrees.
> A difference of 20 degrees as is shown in the attached picture.
>
> The mirror now gets an inclination of 0.5 ( phi - 20 ).
> For latitude 52 this is 16 degrees.
>
> The pattern on the now inclined ceiling also is a polar dial.
>
> I did not look for the extreme limits, but just gave it a chance.
>
> Following the same procedure the polar dial is cut off at about 3.5 hours
> before and after noon and it is seen that the mirror is less inside.
> (distance CB ).
>
>  At the left the pattern for a south facing dial though CM with
(pin)gnomon
> CB is drawn.
>
> The mirror is at distance CM from C and that is shown with the line KL.
>
> At summer solstice the mirror will be in the shadow of the edge of the
> ceiling untill about 3.5 hours before noon and is shaded again 3.5 hours
> after noon.
>
> So this configuration will work 7 hours at summer solstice.
> A great improvement compared with an horizontal ceiling.
>
> I only need to rebuild my house.
>
> Best wishes, Fer.
>
> Fer J. de Vries
> [EMAIL PROTECTED]
> http://www.iae.nl/users/ferdv/
> Eindhoven, Netherlands
> lat.  51:30 N  long.  5:30 E
>
>
>
>
>
>

Re: Acadian domestic sundials

[Edley McKnight]

 Hi Steve, Fer, Warren, Dialists all,

I'm remembering more and more regarding notch dials that tell the  number of hours til sunset.

With what I've been reading lately of all the richness in the NASS  repository CD, much of what I was told, but didn't understand at the  time is making a great deal more sense.

I'll explain the basic procedure of what I've been told as the main  ideas and then expand on them.

I was told in other terms, but it seems to be easier to relate to an  article written in 1998 by Javier Moreno Bores in the NASS Compendium  of June of that year called "A NEW FAMILY OF SUNDIALS WITH CONICAL  GNOMON".  In that article he covers a number of dials giving Italian  and Babylonian hours using cones as the gnomons.  The particular dial  of interest is the horizontal dial.

As he explains this:
1. First create a standard horizontal dial for the latitude with half  hour lines.
2. Create a cone with an included angle of twice the latitude.
3. Place the cone in place of the gnomon on the horizontal dial with  the point of the cone pointing due south  touching the point all the  lines come together and the cone axis then parallel with the earth's  axis and in contact with the substyle area.
4. Each half hour line extending to the west of the cone is where the  cone's shadow will mark the hours before sunset starting from close  to the cone and moving outward.

Now,  take a flat thin blade and place it in contact with the cone  and the sharp edge in contact with the line of a given hour before  sunset and apply pressure along the plane of the knife forcing it  into the surface some considerable distance and rock it slightly to  open a kerf or deep narrow notch which now, when the sun's light  fills it fully indicates that hour before sunset.  If the surface was  of limited depth the knife could be forced all the way through  leaving a thin slit.  If all the hours were so made into slits then  if this board were lifted up a bit the light would shine all the way  through and make a lines of light on a surface below which would  indicate, again, the hours before sunset.  This board could be used  as a template to mark the lines on another surface.

Now, starting with a fresh surface, If one slowly brought the knife  to the proper angles for say each of the six hours before sunset as  it was drawn along the cone we would have a long curving line with  the angle of the kerf varying as the angle on the surface changed.   If this were done slowly enough the one line would be able to tell  all the times in the interval from 6 hours before sunset to sunset.   If one were a master wood carver then one could even remember that  cut and be able to make it whenever and wherever we wanted.   With  skill the hours could be made to be linearly spaced along this curve  and so marked.

An exact mirror curve could be cut on the other side of the cone and  thus mark all the Babylonian hours or hours after sunrise.

This sounds like a pretty nice sundial, I'll try making it myself.

Apparently this approach will work well only in the middle latitudes  from say 20 to 66 degrees.

I hope this sounds like as much fun as it does to me ( after a mostly  sleepless night thinking about it. )

Good luck in your search, I hope this is what you are looking for.

Edley