Can
You Really Tell Time with a Sundial?
By Jeanette Joy Fisher
Sundials have been around since the days of the
Sumerians, some five thousand years ago, and were
the earliest known means of keeping time. The
first sundials were probably just rods or sticks
pounded into the ground, and the shadows cast by
those vertical rods (called a gnomon) allowed
ancient people to know what time of day it was.
The Greeks and Romans took the basic concept and
refined it, using various different shapes of
dials to not only tell the time of day, but also
what time of year it was by the shadow cast by the
gnomon into a cleverly designed bowl. As the
centuries went by and technological advances made
clocks and watches commonplace, sundials were
largely relegated to decorative status in gardens.
As to whether you can actually tell time by using
a sundial, that's a bit trickier. Modern clocks
and watches assume there are exactly twenty-four
hours in a day, but isn't the case, which is why
we have to add a 29th day to the month of February
every four years.
That may be convenient for modern society, but it
means that a sundial, which expresses the true
nature of Earth's elliptical orbit around the sun,
is sometimes fast and sometimes slow, depending
upon the season. Deep in February, for example, a
sundial would be about fifteen minutes slow
according to modern timepieces. However, in
November, a sundial would appear to be as much as
seventeen minutes fast. Such deviation could cause
serious problems for the modern world, which
depends upon accurate, uniform time throughout the
globe. (Interestingly, sundials actually are
correct on four days of every year, although those
dates may vary: April 15, June 14, September 2,
and December 25.)
Of course, your sundial must be oriented
correctly. The numbers corresponding to the shadow
of the gnomon need to be calibrated according to
the specific longitude and latitude of your
location. There are various sites on the Internet
that can help you set your sundial up correctly.
There are also sundial enthusiasts around the
world who have formed organizations that will be
more than happy to help you get your sundial up
and running. Just type "sundials" into your
browser and you'll find lots of information.
So the question remains: can you really tell time
with a sundial? The answer is an unqualified
yes--and no--depending upon who you talk to.
Copyright © 2006 Jeanette J. Fisher
Jeanette Fisher, author of interior design,
real estate, and credit books teaches five ways to
makeover your home and office for happiness and
productivity. Free Design Psychology information:
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Permission granted to publish this article as
long as the bio remains intact with a live link to
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