How to Build a Sundial

Sundials are the oldest known method of keeping track of time.  To build one from scratch, it will help if you or your adult helper knows how to use a protractor, because you have to measure many angles precisely. 

If you prefer, you can look on the Internet for a pre-made sundial plan and use it, but quite often you will need to change it a bit to apply to your own latitude or location on earth.
 
During the year, it is possible for your sundial to be out an hour due to daylight savings, and also up to another 15 minutes because of changes in the earth’s orbit around the sun for the seasons.  This CAN BE adjusted with some longitude corrections, but it gets pretty complicated, so the instructions here are for a basic sundial created with a protractor that is useful to read standard time. 

It’s a lot of fun to read time from shadows!

You Will Need:

• 2 pieces of sturdy cardboard, not too thick, about 8 x 10 inches

• Protractor (or a printed diagram of sundial base)

• Pencil

• Ruler

• Tape or glue

• Scissors

• Latitude for your location

• Know where north is

• A sunny day

Instructions

1. On a full sheet of cardboard, draw a horizontal line (straight across), very near the bottom on the short side.

2. Write the number 6 at both ends of the line.  This represents 6 am on the left and 6 pm on the right.

3. Measure exactly halfway across the card and draw a vertical (up and down) line from your base 6 o’clock line to the top of the cardboard.  Mark this at the top with 12.  Your sheet now is basically showing an upside down capital T.

4. Lay your protractor along the bottom line with 90 degrees resting at the joining of the 6 and 12 o’clock lines.  With your pencil, carefully mark every 15 degrees starting with the base 6 am line and working in a curve toward the middle upright line and past it to the 6 pm line.  (This is the angle you would change slightly if you were adjusting for longitude or season.)

5. From the very corner of the 12 o’clock line meeting the 6 o’clock line, draw lines outward to meet your 15-degree marks on both left and right sides.  This should divide your page into 12 equal sections. Each section is an hour of time. You can label each line from left to right with the hour.

6. Cut the top off the second piece of card to make it shorter (so it is still 8 inches across, but now only about 6 inches high). 

7. Using the bottom right hand corner as 90 degrees, mark an angle at that corner that is the same as your latitude.  If you live at 45 degrees latitude, the angle will be 45. If you live at 52 degrees latitude, the angle will be 52, and so on. Draw a line from that bottom right corner through your angle marking to the top of the card and then from that spot on the top of the card, draw a line straight down to form a triangle shape.  With it laying flat in front of you, and your latitude angle on the right, the bottom left hand corner now will show a 90-degree angle.

8. Cut out the triangle carefully.  This will be your gnomon, which is the name for the sundial pointer or shadow-caster.

9. The special latitude angle has to be placed at the bottom of the sundial where the 6 and 12 lines meet.  The gnomon sits directly along the 12 o’clock line.  You must now use tape or glue to secure the gnomon triangle to this line. If it is crooked, your time readings will be wrong, so use as much tape or glue as necessary to keep it straight on the line and upright. Let the glue dry if you used any.

10. It’s ready!  Take your sundial outside and lay it on a flat surface in a fairly open area so you don’t have extra shadows falling on it.  We suggest you do this for the first time in the mid-morning or the mid-afternoon and not at noon so you can best see how it works.  Point the gnomon (12 o’clock line) to North.  The shadow it casts on the base lines should be the time of day!  (Remember it can be off as much as an hour for Daylight Savings and another 15 minutes either way depending on the season.)

Amazing!