Hello John, Yes, this is a puzzle. The sun on the solstice, 21 June, is at its lowest altitude in the southern hemisphere. The noon altitude would be 47°. The sun would rise and set on that day farthest to the north. This is an appropriate new years day in the southern hemisphere to celebrate the return of the sun as our new year in the north starting at the winter solstice. None of these 21 June observations seem to relate to the "sundial".
However other seasonal markers would be obvious with this sundial. One is the winter solstice 21 Dec. On that date at the Tropic of Capricorn the sun at noon would be directly above this sundial, casting no visible shadow. This would explain the vertical orientation of the gnomon as the shadow could be seen getting shorter as noon approaches and longer in the afternoon. The sloping east west gnomon could be used to note an approximate midway point between the equinox and the solstice. When does the sun line up due east and west at an altitude of 23.5°? The equation for the prime vertical, the east west meridian, Sin Alt = Sin Dec / Sin Lat. This resolves to Sin Dec = Sin23.5 x sin 23.5 and gives the declination as -9.15°. The east west sun along the line of the sloping gnomon occurs around 17 Oct and 25 Feb. Perhaps these were significant dates for the ancient culture in the area. Pre-Christian cultures in Europe had such mid-season markers, Samhain 1 Nov and Imbolc 2 Feb. were a couple of the names. A residual in Christian cultures is Michaelmas and Candlemas The gnomon could also indicate the equinoxes as the sun rises due east and sets due west in line with the gnomon. For early cultures marking the calendar with seasonal markers was much more important than measuring the time of day. Regards, Roger Bailey From: John Goodman Sent: Sunday, April 24, 2016 8:31 AM To: Sundial List Subject: Tropic of Capricorn sundial I was recently in northern Argentina at the Tropic of Capricorn. I saw a structure there that has been described as a sundial but I have trouble understanding how it could work. I'm attaching a small photo of the gnomon, which is angled at roughly 23.5 degrees. So far so good. What confuses me is that the gnomon is aligned along the east/west axis, which you can see by the Google Maps satellite view shown for the coordinates 23°26'52.1"S 65°21'06.0"W I've also read this description of the marker, automatically transited from Spanish: Generally, this place is chosen so that the natives of here come and celebrate the Inti Raymi, thanking the Sun on June 21, as the Incas used to do many years ago. They await the arrival of the Sun which for them is a new year. Would an east/west orientation be appropriate for a monument marking the June solstice south of the equator? Thanks for your help deciphering the design, John -------------------------------------------------------------------------------- --------------------------------------------------- https://lists.uni-koeln.de/mailman/listinfo/sundial -------------------------------------------------------------------------------- No virus found in this message. Checked by AVG - www.avg.com Version: 2016.0.7539 / Virus Database: 4556/12091 - Release Date: 04/24/16
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