When I have a clock and not a sundial, clock time has to be converted into sundial time (Local True Solar Time) to make it day-relevant.
So, if you make a sundial, shouldn't it just show sundial time? Isn't that really what a sundial for--showing Local True Solar Time? You could make a correction-table to convert sundial-time to clock-time--consisting of the EoT, with the longitude-correction added to it for converting from sundial time to clock time. ...and display it beside the sundial. By the way, when I said that a Disk Equatorial is incomparably easier to make than a Band or Cylinder Equatorial, of course should have added "...unless you already have a cylinder or a band, and a means to make a hole in it, to make a circumference hole-nodus. Of course such a dial can only show 12 hours of time, but that can be remedied by having more than one circumference-hole nodus. I don't know the right terminology for what I call a Band-Equatorial or a Cylinder-Equatorial. If the band is wide enough for a circumference hole-nodus to cast it light-spot on the band all year, so that the band has a width equal to D*2tan(obliquity), giving it a width nearly equal to half its diameter, maybe that's the practical-difference-point at which a Band-Equatorial becomes a Cyllinder-Equatorial. As I understand it, "Equatorial Dial" usually refers to a Disk-Equatorial. I call it the Cylinder and Band versions Equatorials because they measure time in the same direct way that a Disk-Equatorial does. ...but their dial-surface is parallel to the Earth's polar-axis so someone could argue that they should be called Polar Band or Cylinder dials. So what are they correctly called? Michael Ossipoff .. On Wed, Oct 18, 2017 at 3:29 AM, Nathaniel Shippen <shippenn...@gmail.com> wrote: > Well, my first attempt at a sundial is about the simplest you could > imagine. However, I did follow Albert Waugh's suggestion in "Sundials: > Their Theory And Construction" and offset the time marks to Hawaii Standard > Time, so I only have to keep the daily Equation of Time value in mind. Note > that the 12:30 mark is almost vertically below the gnomon. At my location > near Honolulu mean solar time is 32 minutes behind HST (GMT - 10). In fact > until after World War 2 clocks in Hawaii were set to GMT - 10:30, much > closer to mean solar time throughout the state. In 1947 Hawaii was > shoehorned into the GMT - 10 timezone also used in the Aleutian Islands. > > https://en.wikipedia.org/wiki/Hawaii%E2%80%93Aleutian_Time_Zone > > Nathaniel Shippen > > On Wed, Oct 18, 2017 at 3:53 AM, Michael Ossipoff <email9648...@gmail.com> > wrote: > >> But, if you're willing to give up the Horizontal-Dial's advantages, then >> an Equatorial-Dial has the following advantages: >> >> 1. Its equally-spaced hour-lines allow perfectly accurate linear >> interpolation of the time, when the shadow is between hour-lines. >> >> (But, when usiing pocket horizontal tablet-dials, linear interpolation >> gave results accurate with 3 minutes, when only the hours and half-hours >> were marked. So interpolation with unequally-spaced hour-lines doesn't seem >> a problem.) >> >> 2. Its principle is obvious. The Horizontal-Dial's construction-principle >> isn't difficult to explain, but the Equatorial's construction-principle is >> obvious at a glance. It would make perfect sense to anyone, without any >> explanation. >> >> (By the way, it's true that a Bifilar Dial shares the advantage of >> equally-spaced hour-lines. But it only tells time for part of the day, >> because, when the Sun is low, the shadow of interest won't be on the >> dial-plate.) >> >> Of course a two-sided Disk-Equatorial is incomparably easier to construct >> than a Band-Equatorial or Cylinder-Equatorial. ...if you don't mind the >> fact that a Disk-Equatorial can only be read from the north in the summer, >> and from the south in the winter. >> >> Michael Ossipoff >> >> >> >> >> On Mon, Oct 16, 2017 at 8:48 AM, Brad Thayer <wissenschaft...@verizon.net >> > wrote: >> >>> I am looking to make a hemicyclium-type sundial (half-hemisphere) in a >>> metal working class. What little I can find on them says they are >>> inaccurate, without being very clear on the problem. It appears to me the >>> only issue is it needs to be tilted so that the gnomon aligns with the >>> Earth’s rotation axis; thus the half-bowl faces south and the gnomon points >>> south, but the end of the gnomon that attaches to the bowl points north. >>> Am I missing anything? I am also looking to use an analemma-shaped gnomon >>> to cast the shadow on the bowl, and at least month lines for the solar >>> elevation. The bowl will also have a rod and bracket on the bottom to >>> allow it to be rotated for daylight-savings time and for local longitude >>> corrections. >>> >>> >>> >>> Thanks in advance -- Brad >>> >>> --------------------------------------------------- >>> https://lists.uni-koeln.de/mailman/listinfo/sundial >>> >>> >>> >> >> --------------------------------------------------- >> https://lists.uni-koeln.de/mailman/listinfo/sundial >> >> >> >
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