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Make Your Own Sundial!
by Tony Flanders
S&T: Craig Michael Utter
Sundials are amazingly simple yet effective devices. They range from
sticks planted in the ground to precision-machined marvels costingthousands of dollars. The design shown here can be constructed in minutes
from materials lying around your house, but its surprisingly accurate.
First, download one of the PDF files listed below and print it out. You will
needAdobe Readerto do this; clickhereif you havent already installed it
on your computer.
Northern Model(PDF)
Southern Model(PDF)
Sundials need to be adjusted according to your approximate latitude
how far you are north or south of the equator. If you dont know your
latitude, you can find it on most maps, or at one of these websites:
U.S. Census Bureau(U.S. Only).
Heavens Above
Cut and fold the printout according to directions printed on it. You might
want two copies so that you can work on one while reading the directions
on the other. The only hard part is pushing the pencil point through the
center of the small circle. It helps to twirl the pencil as you push.
http://www.adobe.com/products/acrobat/readstep2.htmlhttp://www.adobe.com/products/acrobat/readstep2.htmlhttp://media.skyandtelescope.com/documents/sundial_n+.pdfhttp://media.skyandtelescope.com/documents/sundial_n+.pdfhttp://media.skyandtelescope.com/documents/sundial_s.pdfhttp://media.skyandtelescope.com/documents/sundial_s.pdfhttp://www.census.gov/cgi-bin/gazetteerhttp://www.census.gov/cgi-bin/gazetteerhttp://www.heavens-above.com/SelectTown.aspxhttp://www.heavens-above.com/SelectTown.aspxhttp://www.heavens-above.com/SelectTown.aspxhttp://www.census.gov/cgi-bin/gazetteerhttp://media.skyandtelescope.com/documents/sundial_s.pdfhttp://media.skyandtelescope.com/documents/sundial_n+.pdfhttp://www.adobe.com/products/acrobat/readstep2.html7/30/2019 Make Your Own Sundial
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During autumn and winter, the Sun shines up from below the readout face, and the shadow is visible through the paper.S&T: Tony Flanders
When youre done, the pencil should be perpendicular to the sundials face
(notto the base). If the pencil wants to topple over, try taping the whole
thing to another piece of paper or (better) to a sheet of cardboard.
Mounting the sundial on cardboard also makes it easier to carry around.
Cereal boxes are a great source of free cardboard.
Point the pencil due northor south if you live in the Southern
Hemisphere. You can use a compass or a map to determine the proper
direction, or you can just orient the sundial so that it agrees with your
watch. (Subtract one hour from the watch if youre on daylight-saving
time.) Then watch the shadow on the sundial change as the Sun moves
from east to west over the course of the day.
This design is called an equatorialsundial because the face with the
numbers is parallel to Earths equator. Its easiest to use at midwinter and
midsummer, and hardest near the equinoxes around March 20th and
September 23rd.
How Equatorial Sundials Work
The horizontalsundial, with a readout face parallel to the ground, is the
most common designthe one thats often found in garden stores.Horizontal sundials are easy to use but tricky to design and build.
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During the spring and summer, the Sun shines down on the readout face, and the shadow falls on the top.S&T: Tony Flanders
The model youve just built is called anequatorialsundial because its
readout face is parallel to Earths equator. Conceptually, its the simplest
design, but it suffers from one practical disadvantage. Depending on theseason, the pencils shadow may fall either on the top or the bottom of the
readout face. Because the face is made oftranslucent paper, its easy to see
the shadow even when its on the underside. This would be extremely
awkward if the face were made of metal.
To see how this sundial works, imagine first that you lived at the North or
South Pole. In that case, a stick planted upright in the ground would
form both a horizontal andan equatorial sundialthe two designs being
identical at those locations. During the spring and summer, the Sun wouldrotate a full 360 around you every day, staying the same height above the
horizon all the time. The sticks shadow would behave exactly like the
hour hand on a 24-hour clock, staying the same length all day long while
rotating at a constant rate. During autumn and winter, the Sun would never
rise, and your sundial would be useless. But you would be too cold to care.
The pencil in the sundial youve just built is parallel to that stick at the
Pole, and the readout face is parallel to the ground there. So the pencils
shadow behaves exactly like the shadow of the stick at the Pole, exceptthat the shadow is visible even in the winter. Thats because unlike our
planet, the sundial is hollow, allowing the Sun to shine up from below.
Do you find that your sundial isnt as accurate as you would like? That
may be partly due to construction problems. Paper isnt very rigid, and no
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matter how carefully you do the folds, the sundial wont hold its shape
perfectly. But there are also some more fundamental reasons why sundials
and clocks tell different time. For more information, see our articleTime
and the Amateur Astronomer.
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