Make Your Own Sundial

7/30/2019 Make Your Own Sundial

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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.html


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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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Make Your Own Sundial