Some years ago (1999) there was a short discussion, on Italian Mailing List, on the sundials at the Pole: I tried to translate in (very bad) English my considerations, that I sent also to the List [email protected]
I send again hoping not to bore those who have already read them and also to try to help understand why at the poles things are not as in other places of the Earth :-) There (and only there) we don’t have the directions East, West, since all directions indicate the North. There we have not a longitude value: you can choose the one you want. The day starts when you want. Etc. All because the poles are singular points ! --------------------- - I refer to the South Pole and, obviously, to the season in which the Sun is there visible. In my opinion an equatorial sundial carried to the Pole and placed horizontal on the ground (? ), with its style vertical, marks "the Pole’ hour" no matter how it is rotated in its positioning. In other words if, after having arrived to the Pole, I draw on the earth (? ) a line passing for it, it marks the noon whatever is its direction. Obviously if I draw the line in the direction of the Greenwich or of the New York meridian, my horizontal sundial will mark the time of Gr. or of NY but, for me, to do this is a "straining". It is as if I change the hour of my clock to let it mark the Gr. or the of N.Y time : it would not mark anymore the time of the place where I am, but that of another place. In my horizontal clock at the Pole the meridian line that I take (at random) marks “my” noon, that perhaps coincides with that of Gr. or of NY. This oddity depends obviously by the fact that the Pole is a singular point for the system of spherical coordinates that we use. For a hypothetical inhabitant of the Pole (that would have to be extremely thin and threadlike) it doesn't exist any astronomical phenomenon that can be used to mark the beginning of the day or the instant from which to start a whatever system of hours. For our Mr. Thin it would not exist therefore the concept of beginning of the day, of noon, of dawn, of sunset and of midnight (in the half the year when he remains in the dark). Therefore the choice of the beginning from which to count the hours is, for him, perfectly arbitrary (perhaps I would take the direction where my eyes are turned in the moment of my awakening, he perhaps like best other lines) Previously, in selfish way, I have spoken of myself that reaches the Pole with an equatorial sundial under my arm. If I were less selfish and invited you all to make a small trip down South, only I could place myself exactly at the Pole and put my feet on the little cross that marks it (I have thought to a little cross because for my myopia certainly I would not succeed in seeing an infinitesimal point marked on the ice !) : actually, because of my not negligible diameter, I am not sure that I would succeed to put my person in the place of Mr. Thin. I would also be very uncomfortable because or I would be crossed by the gnomon or I would have to put it exactly in the center of my head. All you would be near me but not at the Pole and therefore each of you could determine the instant of the diurnal culmination of the Sun and therefore the direction of the noon. Each of you would have the noon coincident with that of the meridian on which he is placed, while I could choose my noon as I want : in any case a certain amount of diplomacy would be necessary to get on well. We would have to have a lot of patience also to understand us if, for instance, we see an airplane that passes exactly above my head following a circum-polare course. I would say that it comes from North and it goes toward North, one of you would say that no, it comes from South and it goes toward North, another that it comes from East and it goes to West and so away. Certainly the life of Mr. Thin has some disadvantages (to keep always vertical without any movement and with the only possibility to turn on himself, the be always alone - in a place with infinitesimal dimensions there is not a lot of space), but also it offers some remakable advantages , if he is a dialist. At the Pole it is always noon or the hour that he wants; there is always only one cardinal point - the North ; the horizontal, equatorial, analemmatic, azimuthal sundials have all the same simple drawing; there are not the italic and the babilonic hours; the temporary hours are always long exactly as two standard hours; is not necessary to worry for the time zones, the Longitude correction and others complications ; also the constructions of the analemma and of the astrolabe are very simple. Unfortunately (? ) the altitude sundials, as the portable ring sundials, the quadrant s., the shepherd s., etc. , could not work. It is this the only kind of solar clock that, in my opinion, doesn't work at the Pole. The height sundials in fact would have only one hour line and would always mark the same hour: perhaps this is the " true hour of the Pole" (which? ) . I think that Mr. Thin is not very annoyed for this lack: because he cannot move from the Pole he is not very interested to portable sundials Gianni Ferrari ------------------------------ - 2013/4/10 Beverly Stimpson <[email protected]> > > Dear List Members (and experts!), > > I am a new member to this Mailing List - a school-teacher who can see the > several curriculum benefits, of using sundials in (mainly Primary) schools. > > One of my pupils recently asked me a question, which seemed simple - but > after thinking about it, now I am not so sure it has an obvious answer! > > > Basically, is geographic East/West always at exact 'right-angles' to the > direction of North/South - or is this affected by Latitude of location? > > On magnetic compasses, plus most maps (depending on the projection used), > East/West is certainly at 90 degrees to North/South - but at (say) the > North and South Poles there is no East or West direction at all, or are > those locations just 'special cases' (being the exception to the rule)? > > > That is what made me wonder, if East/West might depend on the Latitude. > > To keep things simple, I am only thinking about horizontal surfaces. > > > I shall look forward to your replies, explaining whether East/West is > always at 'right-angles' to North/South (or not, as the case may be). > > > Thanks, > > Bev Stimpson. > > > -- > --------------------------------------------------- > https://lists.uni-koeln.de/mailman/listinfo/sundial > > -- --------------------- Ing. Gianni Ferrari Lat. 44;38,18.5N Long. 10;56,05.3E [email protected]
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