Re: On northern vs. southern dials

[fer j. de vries]

Anselmo et All,   I think the answer to your question is latitude 45 degrees.   At any place the sun is half a year above the horizon. This also means that the sum of the hours that a north facing wall and a south facing wall catch the sun also is half a year.   So we have to look for the latitude where a north facing dial catches the smallest amount of the sun ( or where a south facing dial gets the highest amount of the sun ).   At the pole the sun shines at the north side for 50% as you said. Going to lower latitudes this percentage decreases to a minimum but than increases to the same amount of 50% again at the equator as you also said.   At first glance I should answer that minimum than will be just between at latitude 45 degrees.   If this symmetry is true this also would mean that at latitude X and at latitude 90 - X the number of hours of sunshine on a north facing dial is equal. ( and the numbers of hours of sunshine on the south dial also is equal )   And indeed this is true.   Have a look at the attached pictures of a north facing dial at 23.5 and at 66.5 degrees. You may see that the amount of sunshine is equal for both latitudes. And this equality is present for any couple of latitude X and 90 -X.   So I think that the answer to your question is 45 degrees.   Best wishes, Fer.   Fer J. de Vries [EMAIL PROTECTED] http://www.iae.nl/users/ferdv/ Eindhoven, Netherlands lat.  51:30 N      long.  5:30 E ----- Original Message ----- From: Anselmo Pérez Serrada To: Sundial, Mailinglist Sent: Sunday, March 03, 2002 5:02 PM Subject: Re: On northern vs. southern dials Hi Mike, hi diallists,      When I said a sundial in the North Pole I meant a sundial, say, at 1 cm from it. There the concept of North still makes sense and it is obvious that there there are as many hours of sunlight in the northern side than in the southern side in the course of a year. And we can make the same reasoning for a dial in the Equator: there we have the same result, but with a different distribution along the days.   As for the 'not-50%+50%' question, you may look at two things to realize that it is not like this in all latitudes:    1st Take a glance at the lines in a classical azimuthal sundial (you can make one with Sonne program).    2nd (and more convincing ;) just ask how much does it cost a flat or a house oriented southwards and another one oriented northwards... Where I live the difference is no less than 30000 euros!   I do believe (David Pratten said something like this) that the bigger differences occur close to the the Arctic Circles and to the Tropical Circles, but I can't prove it. I suppose that in the end I'll have to apply brute force but I think as well there must be a better way to prove it.   Anselmo ----- Original Message ----- From: The Shaws To: sundial@rrz.uni-koeln.de Sent: Sunday, March 03, 2002 1:54 PM Subject: RE: On northern vs. southern dials Thinking about this question a little more - during the course of a complete year, doesn't every point on Earth get 50% light and 50% dark? So, the further North (or South) you go, the more of the 50% shines on the South (or North) facing wall. So the North (or South) pole is the place to go to get the maximum light shining on the South (or North) facing wall.   Mike Shaw http://homepage.ntlworld.com/jmikeshaw/ N 53º 21' 24" W 03º 01' 47" Wirral, UK.   Attachment converted: Macintosh HD:66-5-n.gif (GIFf/JVWR) (0003E06C) Attachment converted: Macintosh HD:23-5-n.gif (GIFf/JVWR) (0003E06D)