vikings and cloudy skies

[sasch stephens]

This is part of an email that I sent out to the sundial group in 2013.
I'm glad to see that the subject is getting some play.  The Vikings
may have been way ahead of us.  

sasch stephens

http://www.livescience.com/16831-viking-sunstone-crystal-compass.html

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RE: Clouding the issue

[Neil Graham]

I am trying to make contact with the Sundial organisation without sending an 
email to everyone on the circulation list for the group.
I have enjoyed receiving emails from the group over at least a decade.
I am due to retire, and I would like the Sundial group to send their emails to 
another email address than where they have been sent till now. That address is  
  drangra...@gmail.com
I look forward to receiving the organisation’s emails in the future.
A Neil Graham.

From: sundial [mailto:sundial-boun...@uni-koeln.de] On Behalf Of Roger Bailey
Sent: Monday, 30 March 2015 5:24 p.m.
To: peter.ma...@adelaide.edu.au; sundial@uni-koeln.de
Subject: Re: Clouding the issue

Hello Peter and all,

Yes, clouds are a significant, perhaps the overwhelming issue with sundials. 
Night knocks out half the time and clouds at least half of the remaining 
daylight hours. Our BSS colleagues know the problem. The most common sundial 
motto is "I count only the sunny hours". This is a truly defeatist attitude in 
these days of technology. Can we do better? The effects of clouds are subtle. A 
slight overcast can destroy the contrast required to read a sundial. Such 
sunlight, not enough to cast shadows can burn pale skin. Fleeting clouds cause 
the shadow to bounce back and forth giving indeterminate time readings 
depending on the side of the sun obscured. I don't think wavelengths are the 
solution. Wavelength effects giving us red sunsets but there seems to be no 
advantage through daytime clouds. But where there is light, there is hope. 
Polarization is detectable through light clouds. Take that old polarizing 
filter from your obsolescent SLR camera or an old pair of Polaroid sunglasses, 
hold towards the sun and turn to see the polarization of the sky. Direct views 
of the sun are not required. Polarized skylight can tell you where the sun is 
when it is obscured. The polarization effect is evident but not distinct. The 
phenomenon exist and is familiar to photographers with polarizing filters, a 
vanishing species. Has the effect been exploited by gnomonists? I don't think 
so. The opportunity remains, a chimera, like analemmatic moondials. I am 
working on the latter for the NASS conference in Victoria BC in June.

Regards, Roger Bailey

From: Peter Mayer
Sent: Sunday, March 29, 2015 3:13 PM
To: sundial@uni-koeln.de
Subject: Clouding the issue

Hi,

In the "Last Word" section of a recent _New Scientist_ Stephen Parish 
raised the question of sundials that might work on cloudy days...Clearly, 
polarisation is possible, but I'm doubtful about shadow casting...
Clouding the issue

  *   18 March 2015
  *   Magazine issue 3013. Subscribe 
and 
save
  *   For similar stories, visit the Last 
Word Topic Guide

Are there any wavelengths at which the sun still casts a shadow when the sky is 
full of clouds? Could I make a sundial that would work on a cloudy day?

Stephen Parish, London, UK

This article appeared in print under the headline "Clouding the issue"
[Issue  3013 of New Scientist 
magazine]

  *   From issue 3013 of New Scientist 
magazine, page 57.
best wishes,

Peter


--

Peter Mayer

Department of Politics & International Studies (POLIS)

School of Social Sciences

http://www.arts.adelaide.edu.au/polis/

The University of Adelaide, AUSTRALIA 5005

Ph : +61 8 8313 5609

Fax : +61 8 8313 3443

e-mail: peter.ma...@adelaide.edu.au

CRICOS Provider Number 00123M

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Notice of Legal Status a

Re: Clouding the issue

[Bill Gottesman]

That is an excellent question!  I have seen this photo before, and never
noticed the numbers running twice in a semicircle.  I, too, am perplexed.
I read about this dial in Hester Higton's book "Sundials at Greenwich."
 The dial operates on two successive polarizations of light - the first
being when light passes through the selenite strips on the glass, and the
second when light reflects at the "the polarizing angle" (Brewster's
angle?) off of the inclined dark glass plate behind the front glass.  "At
all times of the day the radii will appear of various shades of two
complementary colours."  This is different than how a single piece of
polarized film would be used today.

Does this help anyone figure this out?
-Bill

On Mon, Mar 30, 2015 at 3:48 PM, Maes, F.W.  wrote:

> Hi all,
>
> Wheatstone designed still another type of polarization dial than the one
> described by Jim Mahaffey. A specimen is in the collection of the British
> National Maritime Museum in Greenwich, see
> http://collections.rmg.co.uk/collections/objects/265579.html.
> When viewing the celestial pole, the polarization pattern of the sky is
> visible, consisting of two light and two dark regions, which rotate around
> the pole together with the sun.
> What I don't understand from the NMM dial: why does it have twice the hour
> numbers from 1-12 in a semicircle, while the sun rotates through 24 hours
> in a full circle?
> Allan Mills made a modern version, using sellotape instead of selenite;
> see BSS Bulletin 1998 nr. 1. It has one set of 1-12 hour numbers in a
> semicircle, as one would expect.
>
> Best regards,
> Frans Maes
>
---
https://lists.uni-koeln.de/mailman/listinfo/sundial

Re: Clouding the issue

[Maes, F.W.]

Hi all,

Wheatstone designed still another type of polarization dial than the one
described by Jim Mahaffey. A specimen is in the collection of the British
National Maritime Museum in Greenwich, see
http://collections.rmg.co.uk/collections/objects/265579.html.
When viewing the celestial pole, the polarization pattern of the sky is
visible, consisting of two light and two dark regions, which rotate around
the pole together with the sun.
What I don't understand from the NMM dial: why does it have twice the hour
numbers from 1-12 in a semicircle, while the sun rotates through 24 hours
in a full circle?
Allan Mills made a modern version, using sellotape instead of selenite; see
BSS Bulletin 1998 nr. 1. It has one set of 1-12 hour numbers in a
semicircle, as one would expect.

Best regards,
Frans Maes

On Mon, Mar 30, 2015 at 7:06 PM, Ian Maddocks 
wrote:

>  Hi
>
> So what is required is some coating that absorbs in the radio part of the
> spectrum (i.e. not absorbed by clouds), then reemits in the visible? You
> then coat the dial plate and can tell what is in the radio shadow of the
> gnomon.
> OK, that may be a little outside the box
>
> Ian
> Chester, UK
>
>
> --- Original Message ---
>
> From: "Fred Sawyer" 
> Sent: 30 March 2015 13:38
> To: "Roger Bailey" 
> Cc: "Sundial Mailing List" 
> Subject: Re: Clouding the issue
>
>   See "Wheatstone's Polarizing Sundial" by Jim Mahaffey in The Compendium
> 8(2):1-3, Jun 2001.  This is an expanded version of his article that first
> appeared in Optics and Photonic News, 11(7):14-15, Jul 2000.
>
>  Fred
>
>
> On Mon, Mar 30, 2015 at 12:24 AM, Roger Bailey  wrote:
>
>  Hello Peter and all,
>
> Yes, clouds are a significant, perhaps the overwhelming issue with
> sundials. Night knocks out half the time and clouds at least half of the
> remaining daylight hours. Our BSS colleagues know the problem. The most
> common sundial motto is "I count only the sunny hours". This is a truly
> defeatist attitude in these days of technology. Can we do better? The
> effects of clouds are subtle. A slight overcast can destroy the contrast
> required to read a sundial. Such sunlight, not enough to cast shadows can
> burn pale skin. Fleeting clouds cause the shadow to bounce back and forth
> giving indeterminate time readings depending on the side of the sun
> obscured. I don't think wavelengths are the solution. Wavelength effects
> giving us red sunsets but there seems to be no advantage through daytime
> clouds. But where there is light, there is hope. Polarization is detectable
> through light clouds. Take that old polarizing filter from your obsolescent
> SLR camera or an old pair of Polaroid sunglasses, hold towards the sun and
> turn to see the polarization of the sky. Direct views of the sun are not
> required. Polarized skylight can tell you where the sun is when it is
> obscured. The polarization effect is evident but not distinct. The
> phenomenon exist and is familiar to photographers with polarizing
> filters, a vanishing species. Has the effect been exploited by gnomonists?
> I don't think so. The opportunity remains, a chimera, like analemmatic
> moondials. I am working on the latter for the NASS conference in Victoria
> BC in June.
>
> Regards, Roger Bailey
>
>  *From:* Peter Mayer 
> *Sent:* Sunday, March 29, 2015 3:13 PM
> *To:* sundial@uni-koeln.de
> *Subject:* Clouding the issue
>
>  Hi,
>
> In the "Last Word" section of a recent _New Scientist_ Stephen Parish
> raised the question of sundials that might work on cloudy days...Clearly,
> polarisation is possible, but I'm doubtful about shadow casting...
> Clouding the issue
>
>- 18 March 2015
>- Magazine issue 3013 . *Subscribe
>and save*
>
> 
>- For similar stories, visit the *Last Word*
> Topic Guide
>
> *Are there any wavelengths at which the sun still casts a shadow when the
> sky is full of clouds? Could I make a sundial that would work on a cloudy
> day?*
>
> *Stephen Parish, London, UK*
>
> *This article appeared in print under the headline "Clouding the issue"*
> [image: Issue 3013 of New Scientist magazine]
> 
>
>- From issue 3013  of New
>Scientist magazine, page 57.
>
> best wishes,
>
> Peter
>
> --
> Peter Mayer
> Department of Politics & International Studies (POLIS)
> School of Social Scienceshttp://www.arts.adelaide.edu.au/polis/
> The University of Adelaide, AUSTRALIA 5005
> Ph : +61 8 8313 5609
> Fax : +61 8 8313 3443
> e-mail: peter.ma...@adelaide.edu.au
> CRICOS Provider Number 00123M
> ---
>
> This email message is intended only for the addressee(s) and contains 
> information that may be confidential and/o

Re: Clouding the issue

[Ian Maddocks]

Hi

So what is required is some coating that absorbs in the radio part of the 
spectrum (i.e. not absorbed by clouds), then reemits in the visible? You then 
coat the dial plate and can tell what is in the radio shadow of the gnomon.
OK, that may be a little outside the box

Ian
Chester, UK


--- Original Message ---

From: "Fred Sawyer" 
Sent: 30 March 2015 13:38
To: "Roger Bailey" 
Cc: "Sundial Mailing List" 
Subject: Re: Clouding the issue

See "Wheatstone's Polarizing Sundial" by Jim Mahaffey in The Compendium
8(2):1-3, Jun 2001.  This is an expanded version of his article that first
appeared in Optics and Photonic News, 11(7):14-15, Jul 2000.

Fred


On Mon, Mar 30, 2015 at 12:24 AM, Roger Bailey  wrote:

>  Hello Peter and all,
>
> Yes, clouds are a significant, perhaps the overwhelming issue with
> sundials. Night knocks out half the time and clouds at least half of the
> remaining daylight hours. Our BSS colleagues know the problem. The most
> common sundial motto is "I count only the sunny hours". This is a truly
> defeatist attitude in these days of technology. Can we do better? The
> effects of clouds are subtle. A slight overcast can destroy the contrast
> required to read a sundial. Such sunlight, not enough to cast shadows can
> burn pale skin. Fleeting clouds cause the shadow to bounce back and forth
> giving indeterminate time readings depending on the side of the sun
> obscured. I don't think wavelengths are the solution. Wavelength effects
> giving us red sunsets but there seems to be no advantage through daytime
> clouds. But where there is light, there is hope. Polarization is detectable
> through light clouds. Take that old polarizing filter from your obsolescent
> SLR camera or an old pair of Polaroid sunglasses, hold towards the sun and
> turn to see the polarization of the sky. Direct views of the sun are not
> required. Polarized skylight can tell you where the sun is when it is
> obscured. The polarization effect is evident but not distinct. The
> phenomenon exist and is familiar to photographers with polarizing
> filters, a vanishing species. Has the effect been exploited by gnomonists?
> I don't think so. The opportunity remains, a chimera, like analemmatic
> moondials. I am working on the latter for the NASS conference in Victoria
> BC in June.
>
> Regards, Roger Bailey
>
>  *From:* Peter Mayer 
> *Sent:* Sunday, March 29, 2015 3:13 PM
> *To:* sundial@uni-koeln.de
> *Subject:* Clouding the issue
>
> Hi,
>
> In the "Last Word" section of a recent _New Scientist_ Stephen Parish
> raised the question of sundials that might work on cloudy days...Clearly,
> polarisation is possible, but I'm doubtful about shadow casting...
> Clouding the issue
>
>- 18 March 2015
>- Magazine issue 3013 . *Subscribe
>and save*
>
> 
>- For similar stories, visit the *Last Word*
> Topic Guide
>
> *Are there any wavelengths at which the sun still casts a shadow when the
> sky is full of clouds? Could I make a sundial that would work on a cloudy
> day?*
>
> *Stephen Parish, London, UK*
>
> *This article appeared in print under the headline "Clouding the issue"*
> [image: Issue 3013 of New Scientist magazine]
> 
>
>- From issue 3013  of New
>Scientist magazine, page 57.
>
> best wishes,
>
> Peter
>
> --
> Peter Mayer
> Department of Politics & International Studies (POLIS)
> School of Social Scienceshttp://www.arts.adelaide.edu.au/polis/
> The University of Adelaide, AUSTRALIA 5005
> Ph : +61 8 8313 5609
> Fax : +61 8 8313 3443
> e-mail: peter.ma...@adelaide.edu.au
> CRICOS Provider Number 00123M
> ---
>
> This email message is intended only for the addressee(s) and contains 
> information that may be confidential and/or copyright. If you are not the 
> intended recipient please notify the sender by reply email and immediately 
> delete this email. Use, disclosure or reproduction of this email by anyone 
> other than the intended recipient(s) is strictly prohibited. No 
> representation is made that this email or any attachments are free of 
> viruses. Virus scanning is recommended and is the responsibility of the 
> recipient.
>
>
>
> --
>   [image: Avast logo] 
>
> This email has been checked for viruses by Avast antivirus software.
> www.avast.com
>
>  --
>
> ---
> https://lists.uni-koeln.de/mailman/listinfo/sundial
>
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>
> No virus found in this message.
> Checked by AVG - www.avg.com
> Version: 2015.0.5856 / Virus Database: 4315/9410 - Release Date: 03/29/

Re: Clouding the issue

[Fred Sawyer]

See "Wheatstone's Polarizing Sundial" by Jim Mahaffey in The Compendium
8(2):1-3, Jun 2001.  This is an expanded version of his article that first
appeared in Optics and Photonic News, 11(7):14-15, Jul 2000.

Fred


On Mon, Mar 30, 2015 at 12:24 AM, Roger Bailey  wrote:

>  Hello Peter and all,
>
> Yes, clouds are a significant, perhaps the overwhelming issue with
> sundials. Night knocks out half the time and clouds at least half of the
> remaining daylight hours. Our BSS colleagues know the problem. The most
> common sundial motto is "I count only the sunny hours". This is a truly
> defeatist attitude in these days of technology. Can we do better? The
> effects of clouds are subtle. A slight overcast can destroy the contrast
> required to read a sundial. Such sunlight, not enough to cast shadows can
> burn pale skin. Fleeting clouds cause the shadow to bounce back and forth
> giving indeterminate time readings depending on the side of the sun
> obscured. I don't think wavelengths are the solution. Wavelength effects
> giving us red sunsets but there seems to be no advantage through daytime
> clouds. But where there is light, there is hope. Polarization is detectable
> through light clouds. Take that old polarizing filter from your obsolescent
> SLR camera or an old pair of Polaroid sunglasses, hold towards the sun and
> turn to see the polarization of the sky. Direct views of the sun are not
> required. Polarized skylight can tell you where the sun is when it is
> obscured. The polarization effect is evident but not distinct. The
> phenomenon exist and is familiar to photographers with polarizing
> filters, a vanishing species. Has the effect been exploited by gnomonists?
> I don't think so. The opportunity remains, a chimera, like analemmatic
> moondials. I am working on the latter for the NASS conference in Victoria
> BC in June.
>
> Regards, Roger Bailey
>
>  *From:* Peter Mayer 
> *Sent:* Sunday, March 29, 2015 3:13 PM
> *To:* sundial@uni-koeln.de
> *Subject:* Clouding the issue
>
> Hi,
>
> In the "Last Word" section of a recent _New Scientist_ Stephen Parish
> raised the question of sundials that might work on cloudy days...Clearly,
> polarisation is possible, but I'm doubtful about shadow casting...
> Clouding the issue
>
>- 18 March 2015
>- Magazine issue 3013 . *Subscribe
>and save*
>
> 
>- For similar stories, visit the *Last Word*
> Topic Guide
>
> *Are there any wavelengths at which the sun still casts a shadow when the
> sky is full of clouds? Could I make a sundial that would work on a cloudy
> day?*
>
> *Stephen Parish, London, UK*
>
> *This article appeared in print under the headline "Clouding the issue"*
> [image: Issue 3013 of New Scientist magazine]
> 
>
>- From issue 3013  of New
>Scientist magazine, page 57.
>
> best wishes,
>
> Peter
>
> --
> Peter Mayer
> Department of Politics & International Studies (POLIS)
> School of Social Scienceshttp://www.arts.adelaide.edu.au/polis/
> The University of Adelaide, AUSTRALIA 5005
> Ph : +61 8 8313 5609
> Fax : +61 8 8313 3443
> e-mail: peter.ma...@adelaide.edu.au
> CRICOS Provider Number 00123M
> ---
>
> This email message is intended only for the addressee(s) and contains 
> information that may be confidential and/or copyright. If you are not the 
> intended recipient please notify the sender by reply email and immediately 
> delete this email. Use, disclosure or reproduction of this email by anyone 
> other than the intended recipient(s) is strictly prohibited. No 
> representation is made that this email or any attachments are free of 
> viruses. Virus scanning is recommended and is the responsibility of the 
> recipient.
>
>
>
> --
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>
> This email has been checked for viruses by Avast antivirus software.
> www.avast.com
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>
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