Kurt, are you familiar with polarization-type sundials? They work even on overcast days, since the diffused sunlight scattered through the cloud deck retains it's polarization orientation. Of course, instead of looking down at a shadow, you'd be looking up through a tube, through crossed polarizing filters, and then noting the relative angle between the two at the setting of either greatest extinction, or greatest transmission, depending on how that particular sundial was set-up. I've read that the Vikings used crystals with polarizing properties to estimate solar altitudes and azimuths when at sea, on overcast days. I'm at work now and can't do the instant research, but I'm sure there is more on this on the Web somewhere.
From: Canopus56 <canopus56@yahoo.com> I'll probably walk over to the Gallivan Center at around _12:30pm_ to watch the Gallivan sundial tick off local equinox.
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--- Chuck Hards <chuckhards@yahoo.com> wrote:
Kurt, are you familiar with polarization-type sundials? They work even on overcast days, . . . I've read that the Vikings used crystals with polarizing properties to estimate solar altitudes and azimuths when at sea, on overcast days. . . .
Thanks, Chuck. No I hadn't heard of that one. I'll put in on my list of things to do. Thanks for pointing it out. - Canopus56 (Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
--- Chuck Hards <chuckhards@yahoo.com> wrote:
Kurt, are you familiar with polarization-type sundials? <snip>
Offline, Chuck wrote further - --- Chuck Hards <chuckhards@yahoo.com> wrote:
Vikings and Polarization Sundials Bradley E Schaefer; Sky & Telescope; May 1997; 91 <snip>
BTW, this is the same Dr. Schaefer who, while with JPL/NASA in the 1990s, wrote the code for computing stellar telescopic limiting magnitude and skybrightness that is built into most modern planetarium programs. Schaefer, B.E. Feb. 1990. Telescopic Limiting Magnitude. PASP 102:212-229http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=1990PASP..102..212S In the late 1980s and early 1990s he wrote several S&T articles and published BASIC programs in S&T on those topics. Schaefer got his P.Hd at MIT and is now Lousiana State University. << http://www.phys.lsu.edu/dept/direct/schaefer.html >> Schaefer is also the guy who shook up the January 2006 American Astronomical Society meeting with his plot of the redshifts of distant gamma ray bursts that implies that expansion of the universe is accelerating. Schaefer, B. 1/11/2006. The Hubble Diagram to z=6.3 with Swift Gamma Ray Bursts. http://www.phys.lsu.edu/GRBHD/ If his GRB diagram proves up, he may be in line for a Nobel prize, which is fine by me considering all that he contributed to amateur astronomy. - Canopus56(Kurt) __________________________________________________ Do You Yahoo!? Tired of spam? Yahoo! Mail has the best spam protection around http://mail.yahoo.com
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Canopus56 -
Chuck Hards