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" <fwsaw...@gmail.com> Sent: 30 March 2015 13:38 To: "Roger Bailey" <rtbai...@telus.net> Cc: "Sundial Mailing List" <sundial@uni-koeln.de> 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 <rtbai...@telus.net> 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 <peter.ma...@adelaide.edu.au> > *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 > > >
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