RE: Re: Double analemma dials

[Tom Laidlaw]

C


Sent from XFINITY Connect Mobile App

-Original Message-

From: jlcarmich...@comcast.net
To: sundial@uni-koeln.de
Cc: 
Sent: 2016-08-17 3:45:40 PM 
Subject: RE: Re: gn
to use- especially children.  I've seen that even dialists get confused too.

So when I was asked to redesign and install a replacement dial for the
flawed Flandrau Planetarium human analemmatic I jumped at the chance.  I was
told that it is used by mostly elementary schoolchildren.  So I tried to
make it simple, easy-to-read, and user friendly.

I replaced the flawed analemma in the old design with a straight date line
with one week marks on the meridian.  And added Roger's easy to use and
useful Bailey Points.  It is longitude corrected and has 15 minute time
marks.

A user information plaque will have an EOT graph to get watch time (much
easier to use than an analemma).

Here is the result:
http://www.sundials.org/index.php/component/sundials/oneDial/825 


-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of David
Andersson
Sent: Wednesday, August 17, 2016 3:30 PM
To: Sundial Mailing List
Subject: Re: Re: Double analemma dials

In message 
  "fabio.savian"  wrote:

> 
> I know an analemmatic sundial may have sophisticated versions to show 
> mean time, Fred your article is exhaustive, but I think it isn't the 
> better kind of sundial to give this info and to get a precison time 
> (position on the heels or on the middle of the feet, how vertical is 
> the hand rising above the head, estimation of the direction of the 
> shadow, graduations of the minutes, etc).  Conversely it is a very 
> powerful instrument to involve people with gnomonics.
> 
> Anyway I think a simple analemma on the meridian line, without explain 
> its huge limits, is not an option, it is an error.
> 
> thank you, ciao, Fabio
> 
> Fabio Savian
> 


As far as Analemmatic sundials are concerned, surely the person who can be
thanked for making these interactive features so popular all over the world
must be Douglas Hunt of "Modern Sunclocks" in the UK who is responsible for
these being installed in thousands of school playgrounds - plus famous
Stately Homes and even the "Space Shuttle Memorial" (at Racine, Wisconsin),
and his 'Human Sundials' are even mentioned within school-books due to the
many educational benefits.

I do not think that he subscribes to this Mailing List (having been 'chased
away' many years ago, by people who were jealous of his own international
success) - but I seem to remember some discussions on this List around 2
years ago, when Frank King (Chairman of "British Sundial Society") said that
it was an excellent design due to self- adjusting to/from Daylight-Saving
and coping with shadow lengths at different times of year in a better way
than 'traditional' layouts.

His website (www.sunclocks.com), even has a link to Brian Albinson.


Doug's design does NOT use any Analemma, which is as this should be because
(in my personal opinion) it would only 'confuse' the people who simply want
to see their shadow indicating clock time (agreeing with their wrist-watch)
- plus is maybe why "Sunclocks" have become so popular within public areas,
compared with the more conventional sundials which could be costly as well
as subject to theft/vandals.

At the risk of having 'brickbats' thrown at me, I must explain that I have
no "axe to grind" here - but I do think that Doug Hunt could be acknowledged
for the services he has given to advancing both the popularity and
understanding of sundials (of all types), especially with school-children
who will become our 'Diallists of the future".


Sincerely,

Dave Andersson.


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Sombrero as a sundial

[Larry Bohlayer]

This sombrero is a reminder that we should all wear sundial hats to our
next meetings. 20 points for the heaviest version. 50 for wearing it on the
plane.

I am sure that someone has perfected the idea into time readable fashion. A
modified version with a "wakeup hole" to let the sunlight through to one's
skin might actually work.

This shortened url takes you to the Adobe Stock Photo website for the
titled image of "Mexican man having siesta" by Rafael Ben-Ari.
Stock#42495149.

https://goo.gl/CFwZNy



Larry Bohlayer
35.4N, 80.7W
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RE: Re: Double analemma dials

[John Carmichael]

Whenever I include analemmas on sundials, no matter how well I try to
explain their function, people always get confused and find them difficult
to use- especially children.  I've seen that even dialists get confused too.

So when I was asked to redesign and install a replacement dial for the
flawed Flandrau Planetarium human analemmatic I jumped at the chance.  I was
told that it is used by mostly elementary schoolchildren.  So I tried to
make it simple, easy-to-read, and user friendly.

I replaced the flawed analemma in the old design with a straight date line
with one week marks on the meridian.  And added Roger's easy to use and
useful Bailey Points.  It is longitude corrected and has 15 minute time
marks.

A user information plaque will have an EOT graph to get watch time (much
easier to use than an analemma).

Here is the result:
http://www.sundials.org/index.php/component/sundials/oneDial/825 


-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of David
Andersson
Sent: Wednesday, August 17, 2016 3:30 PM
To: Sundial Mailing List
Subject: Re: Re: Double analemma dials

In message 
  "fabio.savian"  wrote:

> 
> I know an analemmatic sundial may have sophisticated versions to show 
> mean time, Fred your article is exhaustive, but I think it isn't the 
> better kind of sundial to give this info and to get a precison time 
> (position on the heels or on the middle of the feet, how vertical is 
> the hand rising above the head, estimation of the direction of the 
> shadow, graduations of the minutes, etc).  Conversely it is a very 
> powerful instrument to involve people with gnomonics.
> 
> Anyway I think a simple analemma on the meridian line, without explain 
> its huge limits, is not an option, it is an error.
> 
> thank you, ciao, Fabio
> 
> Fabio Savian
> 


As far as Analemmatic sundials are concerned, surely the person who can be
thanked for making these interactive features so popular all over the world
must be Douglas Hunt of "Modern Sunclocks" in the UK who is responsible for
these being installed in thousands of school playgrounds - plus famous
Stately Homes and even the "Space Shuttle Memorial" (at Racine, Wisconsin),
and his 'Human Sundials' are even mentioned within school-books due to the
many educational benefits.

I do not think that he subscribes to this Mailing List (having been 'chased
away' many years ago, by people who were jealous of his own international
success) - but I seem to remember some discussions on this List around 2
years ago, when Frank King (Chairman of "British Sundial Society") said that
it was an excellent design due to self- adjusting to/from Daylight-Saving
and coping with shadow lengths at different times of year in a better way
than 'traditional' layouts.

His website (www.sunclocks.com), even has a link to Brian Albinson.


Doug's design does NOT use any Analemma, which is as this should be because
(in my personal opinion) it would only 'confuse' the people who simply want
to see their shadow indicating clock time (agreeing with their wrist-watch)
- plus is maybe why "Sunclocks" have become so popular within public areas,
compared with the more conventional sundials which could be costly as well
as subject to theft/vandals.

At the risk of having 'brickbats' thrown at me, I must explain that I have
no "axe to grind" here - but I do think that Doug Hunt could be acknowledged
for the services he has given to advancing both the popularity and
understanding of sundials (of all types), especially with school-children
who will become our 'Diallists of the future".


Sincerely,

Dave Andersson.


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Re: Double analemma dials

[Helmut Haase]

To all sundialists,
I cannot refrain from inverting Willy's statement. I would say 'Tell the 
people that sundialsgain or lose compared to the time which governs the 
universal laws of physics'.
/Solar/ time (indicated by whatever type of sundial) maps time 
differently and unevenly depending onthe chosen design and on 
timevariant properties of our planet.These properties are 'natural' but 
not essential.


I love sundials very much but I suggest not to tell anyone that our 
quartz watches or atomic clocks gain and lose to the solar (so called 
natural) time. The reference quantity is the physical time. However, 
solar time is a nice, romantic, and historic approximation of time and 
its indicators are fascinating.


Of course the subject is a matter of taste and discussing it can 
degenerate to a round-ender-sharp-ender-contradistinction. My mission is 
just to add to Willy's concern that sundials should not be enobled too 
much by us. The watch should remain the reference instrument to the 
sundial. Anyhow, a sundial with a big error can be an exeeding valuable 
instrument.


Helmut Haase
Lemgo (Germany)



--
Am 17.08.2016 21:15, schrieb Willy Leenders:


To all sundialists,

All that stuff is the result of the irresistible urge to let indicate 
the time of a watch by a sundial.

A sundial is intended to indicate the solar time.
It is the only simple instrument that can do it.
In order to indicate the artificial time, which we have created to 
practical reasons, we have a watch and many other devices.
Tell the people that our watch gains or loses compared to the real 
natural time and that a sundial indicates this natural time, a watch 
the artificial time.


And use your knowledge of mathematics for more useful purposes!

Willy Leenders
Hasselt in Flanders (Belgium)

Visit my website about the sundials in the province of Limburg 
(Flanders) with a section 'worth knowing about sundials' (mostly in 
Dutch): http://www.wijzerweb.be









Op 17-aug-2016, om 19:51 heeft fabio.savian het volgende geschreven:



thank you Willy and Fred for your notes,

I know an analemmatic sundial may have sophisticated versions to show 
mean time, Fred your article is exhaustive, but I think it isn't the 
better kind of sundial to give this info and to get a precison time 
(position on the heels or on the middle of the feet, how vertical is 
the hand rising above the head, estimation of the direction of the 
shadow, graduations of the minutes, etc). Conversely it is a very 
powerful instrument to involve people with gnomonics.


Anyway I think a simple analemma on the meridian line, without 
explain its huge limits, is not an option, it is an error.


thank you, ciao, Fabio

Fabio Savian



Inviato da Tablet Samsung.


 Messaggio originale 
Da: Fred Sawyer >
Data: 16/08/2016 20:37 (GMT+02:00)
A: "fabio.savian" >

Cc: Sundial Group >
Oggetto: Re: Double analemma dials

Hi Fabio

This use of an analemma design on the analemmatic dial has been a 
confusing error that goes back at least to the early 20th century 
introduction of the curve on the dial in Brou, France.  The use of a 
double analemma design with curves calculated to limit error to just 
a few minutes throughout the year goes back at least to 1970 and the 
work of Ken Seidelman at Longwood Gardens in Pennsylvania.  For a 
detailed discussion with equations, etc. see my article "Of 
Analemmas, Mean Time and the Analemmatic Sundial" that you can 
download at https://dl.dropboxusercontent.com/u/4837615/scia7.pdf 
Brian Albinson has taken this idea to heart and, using a slightly 
different approach to the equations, has designed several such dials 
in the Vancouver area.


Fred Sawyer

On Tue, Aug 16, 2016 at 12:23 PM, fabio.savian 
> wrote:



hi all,

I draw inspiration from the image sent by Brian Albison for a
meditation.

I often found analemmatic sundials with the analemma. Has it a
sense ?

Standing on the analemma one can get the right correction for eot
only at noon.
Most of these sundials don't report a warning about it, so the
users get a wrong time al the day, except noon.
Moreover some of them haven't the calendar on the meridian line
but only on the analemma, so the misunderstanding is sure.

The use of a table with the eot should solve the curiosity to get
the mean time, so I wonder why this kind of sundial
is knowspreading with the analemma while it is not suitable for this.
Do you  where this use come from ?

ciao Fabio

Fabio Savian

Inviato da Tablet Samsung.


































 Messaggio originale 
Da: Brian Albinson 

Re: Sunsweep sculpture

[Steve Lelievre]

Thanks to Dave and  Roger for replies to my inquiry about the Sunsweep 
sculpture. I understand that equinocial sunrise and sunset occur due 
East and West and I can live with Dave's suggestion of inferring North 
by imagining a perpendicular to the plane of the sculpture.


That still leaves me flummoxed as to how to get the solstice directions 
from the structure. It's not far from where I live so I'll plan to go 
back there on December 21 to see if I can make sense of it then.


Steve








On 2016-08-16 5:46 PM, Dave Bell wrote:

So, this is the western-most piece of the "arch". Sad that it appears to
have been broken.

Well, if the plane of the arch is oriented E-W, and it's vertical, as it
appears tobe, then the normal to the plane faces North, though no to
Polaris. He equinoctial; sunrises and sunsets would also be due East and
West, so in the plane of the slab.

Dave



-Original Message-
From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Steve
Lelievre
Sent: Tuesday, August 16, 2016 5:19 PM
To: Sundial Group 
Subject: Sunsweep sculpture

Hello,

Has anyone encountered the set of sculptures called Sunsweep by David Barr?
It consists of three pieces at sites along the Canada-USA border (Campobello
NB, Point Roberts WA, Lake of the Woods, MI) and together they are meant to
represent a conceptual arch symbolizing friendship between the two nations.
The 3 sites are geographically interesting - they are reachable by land from
the main part of their respective countries only by travelling through the
other country (pene-enclaves).

I was recently at Point Roberts and saw the piece located there. There is a
plaque indicating that the piece is aligned to the North Star, the equinoxes
and the solstices. I found that the plane of the slab forming the sculpture
is aligned East-West but I could not see anything that matches the other
directions mentioned. Am I missing something? Perhaps the shape causes a
special shadow on the special dates?

You can find photos on the Web, for example at
http://2.bp.blogspot.com/-t9hlFDU5te0/UzWerhh1YLI/mQg/7gPHFqa8TFw/s1
600/Pt+Roberts+Sunsweep.JPG

The outer (upper) curved edge has a curious V profile, with the point of the
V switching from one side of the slab to the other as it progresses over the
length of the curve.  The inner or lower curved edge appears to be
perpendicular to the plan of the slab.  I could not see any markings on the
ground. To me, placement of the ring of stones around the base appears
insignificant.

Any thoughts?

Steve


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Re: Re: Double analemma dials

[David Andersson]

In message 
  "fabio.savian"  wrote:

> 
> I know an analemmatic sundial may have sophisticated versions to show
> mean time, Fred your article is exhaustive, but I think it isn't the
> better kind of sundial to give this info and to get a precison time
> (position on the heels or on the middle of the feet, how vertical is
> the hand rising above the head, estimation of the direction of the
> shadow, graduations of the minutes, etc).  Conversely it is a very
> powerful instrument to involve people with gnomonics.
> 
> Anyway I think a simple analemma on the meridian line, without
> explain its huge limits, is not an option, it is an error.
> 
> thank you, ciao, Fabio
> 
> Fabio Savian
> 


As far as Analemmatic sundials are concerned, surely the person who
can be thanked for making these interactive features so popular all
over the world must be Douglas Hunt of "Modern Sunclocks" in the UK
who is responsible for these being installed in thousands of school
playgrounds - plus famous Stately Homes and even the "Space Shuttle
Memorial" (at Racine, Wisconsin), and his 'Human Sundials' are even
mentioned within school-books due to the many educational benefits.

I do not think that he subscribes to this Mailing List (having been
'chased away' many years ago, by people who were jealous of his own
international success) - but I seem to remember some discussions on
this List around 2 years ago, when Frank King (Chairman of "British
Sundial Society") said that it was an excellent design due to self-
adjusting to/from Daylight-Saving and coping with shadow lengths at
different times of year in a better way than 'traditional' layouts.

His website (www.sunclocks.com), even has a link to Brian Albinson.


Doug's design does NOT use any Analemma, which is as this should be
because (in my personal opinion) it would only 'confuse' the people
who simply want to see their shadow indicating clock time (agreeing
with their wrist-watch) - plus is maybe why "Sunclocks" have become
so popular within public areas, compared with the more conventional
sundials which could be costly as well as subject to theft/vandals.

At the risk of having 'brickbats' thrown at me, I must explain that
I have no "axe to grind" here - but I do think that Doug Hunt could
be acknowledged for the services he has given to advancing both the
popularity and understanding of sundials (of all types), especially
with school-children who will become our 'Diallists of the future".


Sincerely,

Dave Andersson.


-- 
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: R: Re: Double analemma dials

[Willy Leenders]

To all sundialists,

All that stuff is the result of the irresistible urge to let indicate the time 
of a watch by a sundial.
A sundial is intended to indicate the solar time.
It is the only simple instrument that can do it.
In order to indicate the artificial time, which we have created to practical 
reasons, we have a watch and many other devices.
Tell the people that our watch gains or loses compared to the real natural time 
and that a sundial indicates this natural time, a watch the artificial time.

And use your knowledge of mathematics for more useful purposes!

Willy Leenders
Hasselt in Flanders (Belgium)

Visit my website about the sundials in the province of Limburg (Flanders) with 
a section 'worth knowing about sundials' (mostly in Dutch): 
http://www.wijzerweb.be








Op 17-aug-2016, om 19:51 heeft fabio.savian het volgende geschreven:

> 
> thank you Willy and Fred for your notes,
> 
> I know an analemmatic sundial may have sophisticated versions to show mean 
> time, Fred your article is exhaustive, but I think it isn't the better kind 
> of sundial to give this info and to get a precison time (position on the 
> heels or on the middle of the feet, how vertical is the hand rising above the 
> head, estimation of the direction of the shadow, graduations of the minutes, 
> etc). Conversely it is a very powerful instrument to involve people with 
> gnomonics.
> 
> Anyway I think a simple analemma on the meridian line, without explain its 
> huge limits, is not an option, it is an error.
> 
> thank you, ciao, Fabio
> 
> Fabio Savian
> 
> 
> 
> Inviato da Tablet Samsung.
> 
> 
>  Messaggio originale 
> Da: Fred Sawyer  
> Data: 16/08/2016 20:37 (GMT+02:00) 
> A: "fabio.savian"  
> Cc: Sundial Group  
> Oggetto: Re: Double analemma dials 
> 
> Hi Fabio
> 
> This use of an analemma design on the analemmatic dial has been a confusing 
> error that goes back at least to the early 20th century introduction of the 
> curve on the dial in Brou, France.  The use of a double analemma design with 
> curves calculated to limit error to just a few minutes throughout the year 
> goes back at least to 1970 and the work of Ken Seidelman at Longwood Gardens 
> in Pennsylvania.  For a detailed discussion with equations, etc. see my 
> article "Of Analemmas, Mean Time and the Analemmatic Sundial" that you can 
> download at https://dl.dropboxusercontent.com/u/4837615/scia7.pdf  Brian 
> Albinson has taken this idea to heart and, using a slightly different 
> approach to the equations, has designed several such dials in the Vancouver 
> area.
> 
> Fred Sawyer
> 
> On Tue, Aug 16, 2016 at 12:23 PM, fabio.savian  
> wrote:
> 
> hi all,
> 
> I draw inspiration from the image sent by Brian Albison for a meditation.
> 
> I often found analemmatic sundials with the analemma. Has it a sense ?
> 
> Standing on the analemma one can get the right correction for eot only at 
> noon.
> Most of these sundials don't report a warning about it, so the users get a 
> wrong time al the day, except noon.
> Moreover some of them haven't the calendar on the meridian line but only on 
> the analemma, so the misunderstanding is sure.
> 
> The use of a table with the eot should solve the curiosity to get the mean 
> time, so I wonder why this kind of sundial is knowspreading with the analemma 
> while it is not suitable for this.
> Do you  where this use come from ?
> 
> ciao Fabio
> 
> Fabio Savian
> 
> Inviato da Tablet Samsung.
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
> 
>  Messaggio originale 
> Da: Brian Albinson  
> Data: 16/08/2016 18:04 (GMT+02:00) 
> A: Sundial Group  
> Oggetto: Double analemma dials 
> 
> Hi folk
> 
> We have built 3 direct reading mean time double analemma dials, 
> (including the Highlands School dial) in the Vancouver area and are 
> curious to know if any others exist in the world (apart from the 
> Longwood dial).
> 
> Brian Albinson
> 
> Len Berggren
> 
> Vancouver, Canada
> 
> 
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
> 
> 
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
> 
> 
> 
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
> 

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R: Re: Double analemma dials

[fabio.savian]

thank you Willy and Fred for your notes,

I know an analemmatic sundial may have sophisticated versions to show mean 
time, Fred your article is exhaustive, but I think it isn't the better kind of 
sundial to give this info and to get a precison time (position on the heels or 
on the middle of the feet, how vertical is the hand rising above the head, 
estimation of the direction of the shadow, graduations of the minutes, etc). 
Conversely it is a very powerful instrument to involve people with gnomonics.

Anyway I think a simple analemma on the meridian line, without explain its huge 
limits, is not an option, it is an error.

thank you, ciao, Fabio

Fabio Savian



Inviato da Tablet Samsung.


 Messaggio originale 
Da: Fred Sawyer  
Data: 16/08/2016  20:37  (GMT+02:00) 
A: "fabio.savian"  
Cc: Sundial Group  
Oggetto: Re: Double analemma dials 

Hi Fabio

This use of an analemma design on the analemmatic dial has been a confusing 
error that goes back at least to the early 20th century introduction of the 
curve on the dial in Brou, France.  The use of a double analemma design with 
curves calculated to limit error to just a few minutes throughout the year goes 
back at least to 1970 and the work of Ken Seidelman at Longwood Gardens in 
Pennsylvania.  For a detailed discussion with equations, etc. see my article 
"Of Analemmas, Mean Time and the Analemmatic Sundial" that you can download at 
https://dl.dropboxusercontent.com/u/4837615/scia7.pdf  Brian Albinson has taken 
this idea to heart and, using a slightly different approach to the equations, 
has designed several such dials in the Vancouver area.

Fred Sawyer

On Tue, Aug 16, 2016 at 12:23 PM, fabio.savian  
wrote:

hi all,

I draw inspiration from the image sent by Brian Albison for a meditation.

I often found analemmatic sundials with the analemma. Has it a sense ?

Standing on the analemma one can get the right correction for eot only at noon.
Most of these sundials don't report a warning about it, so the users get a 
wrong time al the day, except noon.
Moreover some of them haven't the calendar on the meridian line but only on the 
analemma, so the misunderstanding is sure.

The use of a table with the eot should solve the curiosity to get the mean 
time, so I wonder why this kind of sundial is knowspreading with the analemma 
while it is not suitable for this.
Do you  where this use come from ?

ciao Fabio

Fabio Savian

Inviato da Tablet Samsung.


































 Messaggio originale 
Da: Brian Albinson  
Data: 16/08/2016 18:04 (GMT+02:00) 
A: Sundial Group  
Oggetto: Double analemma dials 

Hi folk

We have built 3 direct reading mean time double analemma dials, 
(including the Highlands School dial) in the Vancouver area and are 
curious to know if any others exist in the world (apart from the 
Longwood dial).

Brian Albinson

Len Berggren

Vancouver, Canada


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Double analemma dials

[Brian Albinson]

Hi Folk

I thank Fred Sawyer for his note on the direct reading mean time double 
analemma dials and will be pleased to provide a note on their 
construction to anyone interested.


Their average error is about 30 seconds; maximum error about 3 minutes.

These dials are quite different from the incorrect and misleading Brou 
analemma dial.


Brian Albinson

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Re: A Strange Rainbow

[John Davis]

Hi Jackie,
I think that what you have there is a circumzenithal arc (CZA), possibly with a 
matching circumhorizontal arc (CHA). They are caused by the sun's rays 
refracting through ice platelets high in the atmosphere. You need the sun low 
in the sky for them to be seen. There are other ice haloes around the sun, 
particularly with 22 degree and 46 degree arcs, but the CZA and CHA are 
generally reckoned to be the most impressive and colourful, second only to the 
normal rainbow. You are very lucky to have seen it (I'm jealous) and 
congratulations for getting a photo.
Regards,
John-- Dr J Davis
Flowton Dials http://www.flowton-dials.co.uk/
BSS Editor http://sundialsoc.org.uk/publications/the-bss-bulletin/


  From: Jackie Jones 
 To: sundial@uni-koeln.de 
 Sent: Wednesday, 17 August 2016, 15:24
 Subject: A Strange Rainbow
   
Dear 
Sundial  folk,  I know this is not really sundial related, but I am sure 
someone will be able to explain this odd rainbow.  The picture was taken 
yesterday just before 6pm British Summer Time on a hot sunny day.  Looking west 
to the low sun, there was a rainbow above it with the ends of it curving 
upwards.   Below it there was a very faint second one in the same curve.  How 
does this happen on a dry day; normally the sun is in the opposite direction to 
the rainbow?  With best wishes in anticipation of an explanation,Jackie  Jackie 
Jones50° 50’ 09” N    0° 07’ 40” W  
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Re: A Strange Rainbow

[Barry Wainwright]

It’s called a circumzenithal arc.

Unlike a normal rainbow, which is caused by total internal refraction within a 
(or, rather, millions of) water droplets, circumzenithal arcs are caused by 
light scattering in ice crystals in the upper atmosphere. They are generally 
only visible on very clear days as any cloud in the lower atmosphere will 
prevent them from being seen.

-- 
Best regards,
Barry Wainwright



> On 17 Aug 2016, at 15:24, Jackie Jones  wrote:
> 
> Dear Sundial  folk,
>  
> I know this is not really sundial related, but I am sure someone will be able 
> to explain this odd rainbow.  The picture was taken yesterday just before 6pm 
> British Summer Time on a hot sunny day.  Looking west to the low sun, there 
> was a rainbow above it with the ends of it curving upwards.   Below it there 
> was a very faint second one in the same curve.  How does this happen on a dry 
> day; normally the sun is in the opposite direction to the rainbow?
>  
> With best wishes in anticipation of an explanation,
> Jackie
>  
> Jackie Jones
> 50° 50’ 09” N0° 07’ 40” W
>  
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> 
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Re: A Strange Rainbow

[Dave Bell]

Typically, this would indicate ice crystals in the upper atmosphere. A normal 
rainbow is formed by water droplets with two internal reflections, so the 
rainbow's light is projected back towards the sun. In this case, the light is 
passed forward through the crystals, at an angle determined by their shape, so 
it appears to be coming from the sun's direction, but offset. 

Dave

Sent from my iPhone

> On Aug 17, 2016, at 7:24 AM, Jackie Jones  wrote:
> 
> Dear Sundial  folk,
>  
> I know this is not really sundial related, but I am sure someone will be able 
> to explain this odd rainbow.  The picture was taken yesterday just before 6pm 
> British Summer Time on a hot sunny day.  Looking west to the low sun, there 
> was a rainbow above it with the ends of it curving upwards.   Below it there 
> was a very faint second one in the same curve.  How does this happen on a dry 
> day; normally the sun is in the opposite direction to the rainbow?
>  
> With best wishes in anticipation of an explanation,
> Jackie
>  
> Jackie Jones
> 50° 50’ 09” N0° 07’ 40” W
>  
> 
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> 
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