Hello Frank,
Thanks for your comments and corrections.
I would have wagered a small amount that I had seen a map showing
average annual sunshine in Vermont to be less than 30% of possible
sunshine. However, I just found a NOAA map which appears to show mean
annual sunshine here as 51 - 55 percent. I take that to suggest a
sundial here might, considering horizon pollution, be sunlit perhaps
20 - 25 percent of the hours during a year.
Anyway, my point remains that, since a sundial functions as a sundial
only part of the time, it really ought to be a pleasant thing to look
at when it's not working.
Best wishes,
Mac
P.S. Do you have an estimate for the percentage of working hours
during a year for a sundial at your location?
Dear Mac
Here in Vermont a sundial is lucky to see the
sun 15% of the hours in a year.
Hmmm, sounds worse than the U.K. :-(
Heck, half of the time it's night!
Interestingly, this isn't true. The number of days from
the March equinox to the September equinox is about 8 more
than the number of days from the September equinox to the
(following) March equinox. This is much more than a
second-order effect!
In the northern hemisphere, therefore, we get more day
than night taking the year as a whole. Down in the
southern hemisphere the reverse is true.
Only on the equator can you say `half the time it's
night' and even there you risk being told by a pedant
that night excludes the period of twilight.
Frank King
Cambridge, U.K.
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