To All:
Thanks to those of you who took time to review and comment on my
sundial page, http://netnow.micron.met/~petes/sundial . I appreciated
your replies.
I do want to specifically respond to Dr. Carlson's reply... he is
absolutely correct in his statement that nearthe summer and winter
solstices you can not simultaneously determine both the date and the
time from this sundial, if both are unknown. From about 10 June to 1
July, and 10 Dec to 1 Jan, you must know the date in order to accurately
tell the time, or you must know the time in order to accurately
determine the date. (And actually with this sundial, at any time, you
must have a general idea of the season in order to determine whether to
use the left or right half of the analemma shadow to indicate the
correct date and time.)
However, I do disagree with his statement that you would be doing well
within these periods to determine the date with an accuracy of 1 week.
On the first and smaller brass sundial I built, with an 11.5" radius (an
equatorial scale of 20 minutes/inch) the date may be determined to
within +- 3 to 4 days during the summer solstice, to within +- 2 to 3
days during the winter solstice, and to within 1 day most other months
of the year. On the much larger park sundial, with a 32.75" radius (an
equatorial scale of 7 minutes/inch) I can easily determine the date to
within 2 days around the summer solstice (if I know the correct time,)
to within 1 day around the winter solstice, and to within 1/4 day during
most other months of the year. Knowing the date within these two
solstice periods, on the park sundial I can still easily read the time
within 20 seconds (on my home sundial the time can be read to within the
minute.) Today for example, when I checked the park sundial, I could
still distinguish today's date exactly (June 7,) but I was a little
disappointed to note at 1:57 this nice sunny afternoon that it was 8
seconds slow in indicating the correct time ;)
My appologies if I appeared to oversell the result on my web pages. As
an engineer, and not a mathematician or a physicist ;) I am usually
thrilled if I am able determine a solution to any problem within 40%,
and then I multiply the answer by a safety factor of 2x or more. So
please forgive me, I have been ecstatic with the results from my park
sundial. It will not get people to the moon, but (ignoring acts of God
and the environment) it will allow them to correctly set their Timex for
the next several thousand years. :)
I guess I should stop now before this e-mail becomes even more pompous
than I intended. I would like to attend the NASS meeting in Seattle
this September, and would like to bring up my brass sundial, hear some
of the presentations, see some of the other work out there, and
hopefully meet a few of you I have corresponded with. Hope to see you
there! Thanks again,
Pete Swanstrom
