Making a Horizontal Sundial for 45 Degrees Latitude
Materials: Novice
for each sundial you will need...
- A small wooden disk
(Craft checkers work great!)
- Approx. 1 yard of cording
(leather, plastic canvas, yarn ...)
- A 3/4"-1" nail
(copper nails are attractive)
- Pencil
- Black Pen
- Scissors
- Index card
- Hammer
- Drill (optional)
- Key chain ring (optional)
If you want to make your sundial into a necklace or keychain you might
want to drill a hole in the checker, or have someone drill the hole for
you, to pass the string through. OR you could screw an eye hook into the
top and pass the string through there. BE CREATIVE, and enjoy!
On a sundial, the gnomon is the piece of the sundial which casts its
shadow onto the sundial face. In our project we will use a copper nail
as the gnomon.
For a horizontal sundial we want the gnomon to be aligned with the South Celestial
Pole so that the sun will rotate
around it when we face our sundial due south.
Preparing the wooden checker
To align our gnomon along this axis we must position it such that it
makes an angle equal to the latitude angle where it will be used with the
horizontal face of the sundial. (See below)
The easiest way to get the nail into the wooden checker at this angle is
to do the following. First, hammer the nail straight into the center of
your wooden checker making sure not to go through the back side.
On an index card draw a line that is inclined from the bottom of the card
at an angle equal to your latitude.
Hammer the nail from the side so that it
begins to bend over.
Place the index card behind the bent nail, with the
start of the line at the base of the nail. Continue to bend the nail over
until it is at the same angle as the line you have on your index card.
Now the nail should be making an angle equal to your latitude with the
base of the checker. It should look like the image above.
If the nail become loose, a little wood glue at the base should secure
it.
Drill a hole in the wooden checker on the opposite side from where the
nail is pointing. Make sure to drill the hole large enough so that the
cord you have chosen will fit through it.
***Note***
If you do this activity with a large group of young children it is often
best to prepare the checkers up to this point ahead of time.
**********
You are now ready to put on the hourlines for the sundial.
Making the hourlines
On a horizontal sundial the position of the lines that indicate what hour
it is also depend on the latitude. To draw the hourlines in the correct
location on the face of your sundial you will need to print the image
below, or reproduce the image by using a protractor. Go to the hourlines
section of the intermediate lesson
to learn
how to create this image on your own or simply print out the image for 45
degrees latitude below.
Once you have a hard copy of the image above, place your wooden checker
on top of the image such that the center of the checker, where the nail
hole is, is directly over the intersection of the horizontal and vertical
lines. The horizontal
line, marked with a six on each side, should run underneath your checker
exactly across the center.
Without shifting the checker, rotate it until the head of
the nail is pointing up the 12 o'clock line, as seen in the image to the
left.
Holding the checker very still, make 13 pencil marks on
the top face of the wood, each mark inline with the appropriate hourline.
It is best to start with pencil so you can redo any mistakes.
Once you have made all of the hour marks go over them in pen and write in
the appropriate numbers. Because the face of our sundial is so small, it
is best to include only a few of the hour numbers, as in the image to the
right.
Finish your sundial by threading the drilled hole with some cording and
tie it off to the desired length.
The moment of truth!
To use your new sundial, take it outside on a sunny day, hold it
perfectly horizontal, and point the head
of the gnomon (nail) due south. The shadow
cast by the gnomon should fall
on the appropriate hourline.
ENJOY!!!!
***ACCURACY***
To compare the time on the sundial you construct to
the time on a clock, there are several adjustments which should be made.
The North American Sundial Society has a nice page which discusses these
adjustments. Visit: Sundial
Time vs. Clock Time .
****REMEMBER****
During daylight savings time you will need to add one hour to the
time on your sundial in order to agree with local "clock" time.
YPOP Homepage
Sundials
Learning Activities
Lesson
designed by
Michelle B. Larson
mlarson@physics.montana.edu