RE: Clouding the issue
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<mailto: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<mailto:peter.ma...@adelaide.edu.au> Sent: Sunday, March 29, 2015 3:13 PM To: sundial@uni-koeln.de<mailto: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<http://www.newscientist.com/issue/3013>. Subscribe and save<http://subscription.newscientist.com/bundles/bundles.php?promCode=8014&packageCodes=PTA&offerCode=Q&cmpid=nsarticletop&intcmp=SUBS-nsarttop> * For similar stories, visit the Last Word<http://www.newscientist.com/topic/lastword> 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]<http://www.newscientist.com/issue/3013> * From issue 3013<http://www.newscientist.com/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<mailto: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 removed by sender. Avast logo]<http://www.avast.com/> This email has been checked for viruses by Avast antivirus software. www.avast.com<http://www.avast.com/> --- https://lists.uni-koeln.de/mailman/listinfo/sundial No virus found in this message. Checked by AVG
Re: Clouding the issue
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
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 <http://www.newscientist.com/issue/3013>. *Subscribe >and save* > > <http://subscription.newscientist.com/bundles/bundles.php?promCode=8014&packageCodes=PTA&offerCode=Q&cmpid=nsarticletop&intcmp=SUBS-nsarttop> >- For similar stories, visit the *Last Word* ><http://www.newscientist.com/topic/lastword> 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] > <http://www.newscientist.com/issue/3013> > >- From issue 3013 <http://www.newscientist.com/issue/3013> of New >Scientist magazine, page 57. > > best wishes, > > Peter > > -- > Peter Mayer > Department of Politics & Inte
Re: Clouding the issue
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 <http://www.newscientist.com/issue/3013>. *Subscribe >and save* > > <http://subscription.newscientist.com/bundles/bundles.php?promCode=8014&packageCodes=PTA&offerCode=Q&cmpid=nsarticletop&intcmp=SUBS-nsarttop> >- For similar stories, visit the *Last Word* ><http://www.newscientist.com/topic/lastword> 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] > <http://www.newscientist.com/issue/3013> > >- From issue 3013 <http://www.newscientist.com/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] <http://www.avast.com/>
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 <http://www.newscientist.com/issue/3013>. *Subscribe >and save* > > <http://subscription.newscientist.com/bundles/bundles.php?promCode=8014&packageCodes=PTA&offerCode=Q&cmpid=nsarticletop&intcmp=SUBS-nsarttop> >- For similar stories, visit the *Last Word* ><http://www.newscientist.com/topic/lastword> 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] > <http://www.newscientist.com/issue/3013> > >- From issue 3013 <http://www.newscientist.com/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] <http://www.avast.com/> > > This email has been checked for viruses by Avast antivirus software. > www.avast.com > > -- > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > -- > > No virus found in this message. > Checked by AVG - www.avg.com > Version: 2015.0.5856 / Virus Database: 4315/9410 - Release Date: 03/29/15 > > > --- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > > --- https://lists.uni-koeln.de/mailman/listinfo/sundial
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 a.. 18 March 2015 b.. Magazine issue 3013. Subscribe and save c.. 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" a.. 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 --- 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. This email has been checked for viruses by Avast antivirus software. www.avast.com --- https://lists.uni-koeln.de/mailman/listinfo/sundial No virus found in this message. Checked by AVG - www.avg.com Version: 2015.0.5856 / Virus Database: 4315/9410 - Release Date: 03/29/15 --- https://lists.uni-koeln.de/mailman/listinfo/sundial
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 <http://www.newscientist.com/issue/3013>. *Subscribe and save* <http://subscription.newscientist.com/bundles/bundles.php?promCode=8014&packageCodes=PTA&offerCode=Q&cmpid=nsarticletop&intcmp=SUBS-nsarttop> * For similar stories, visit the *Last Word* <http://www.newscientist.com/topic/lastword> 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 <http://www.newscientist.com/issue/3013> * From issue 3013 <http://www.newscientist.com/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 --- 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. --- This email has been checked for viruses by Avast antivirus software. http://www.avast.com --- https://lists.uni-koeln.de/mailman/listinfo/sundial