Just got back from Stellafane saw some very interesting Telescopes and Sundials
too.
> Luke Coletti wrote:
> >
> > Note that after twenty years, which falls on a four year boundary from
> > the start, the delta is 1.3 secs.
>
> I believe that the Analemmic gnomon compensates for this. Even though
> the accuracy of the DATE indicated by the sundial changes from year to
> year, I believe this DOES NOT typically affect indication of the correct
> time, except during a solstice, when the date mark must be used to
> accurately indicate the time. A one day date error during the solstice
> would contribute a 30 second time error during the winter solstice, and
> a 13 second error during the summer solstice. Other that that, even
> though the dates shift back and forth around the analemma every year,
> the analemmic gnomon shape still remains the same. Because time is noted
> by the intersection of the edge of the analemmic shadow with the
> equatorial dial time line, regardless of the position of the date marks
> on the gnomon, the sundial should still indicate the correct time even
> though there there is a change in EoT for the same day over different
> years.
>
Pete,
If the EoT has a secular variation so too will the Analemma, the 1.3
secs
after 20 years will indeed affect the shape (although to a very small degree).
> Luke Coletti wrote:
> >
> > Pete,
> >
> > One last thought on your dial, to correct the EoT variation
> > mentioned earlier, you might consider including a four position
> > adjustment mechanism to the Equatorial band.
> >
> > Luke
>
> I have given this some thought, and I can not devise a simple four
> position adjustment mechanism for the Equatorial band. Since the
> analemmic gnomon is a figure-8 shape, not linear, I can adjust the
> equatorial band linearly to be correct for several days, but not for the
> whole year. If I am to improve the accuracy, then I guess that one
> option would be to build 4 interchangeable gnomon plates, (same
> analemmic shape, but with dates shifted 1/4 day,) one for each year of
> the Leap year cycle.
>
Pete,
A cam action with detents should work.
Regards,
Luke Coletti
