Make a Horizontal Sundial - Graphical Method
Horizontal Sundial: the common or
garden sundial with a horizontal dial plate and polar-pointing
Here is another graphical method that
you can use to draw a horizontal sundial. Using this method it easier to
obtain hour lines that are earlier than 7 a.m. and later than 5 p.m.. A
number of steps are similar to the first graphical method presented and
Draw a horizontal line.
Draw a vertical line that passes
through the horizontal line at O.
Select a point C on the vertical
line. This point will be the centre of your horizontal sundial and
eventually all the hour lines will radiate from it.
Draw the line CD at an angle equal to
the latitude (LAT) from OC.
Draw the line OB from O and
perpendicular to line CD. The line OB is the radius of the equatorial
sundial you will be drawing next.
Place your compass point at O and
draw an arc from B until it crosses the vertical line at E. This is
the centre of your equatorial sundial.
Place your compass point at E and
draw a circle starting at O. Notice that OE=OB=R. You have now drawn
the face of your equatorial sundial.
Draw the equatorial sundial hour
lines spaced at
15° in both directions but do not go beyond 9 a.m. and 3 p.m..
If you want smaller time intervals
add more lines. Remember that 15°=60 minutes so 7.5°=30 minutes,
1°=4 minutes. You can figure out the rest.
Extend all the lines to the
From C, the centre of the
horizontal sundial, draw a line to each of the points on the
horizontal line. You have now transferred the hour lines from the
equatorial sundial to the horizontal sundial.
Draw the line JK from the 9 a.m.
point and LM from the 3 p.m. point. These lines are parallel to line
Draw the line OM. This line is
parallel to the 9 a.m. hour line. The distance VO is equal to the
distance VM. This line intersect the 1 p.m. line at point W and the 2
p.m. line at point X.
Place you compass at point V.
Draw an arc at point Y where the
distance VY is equal to VX. Draw a line from point C through point Y
and continue to the line LM. You now have the 4 p.m. hour line.
Draw an arc at point Z where the
distance VZ is equal to VW. Draw a line from point C through point Z
and continue to the line LM. You now have the 5 p.m. hour line.
These steps can be repeated for any
additional hour lines you may want to draw that will indicate time
internals of less than an hour.
Steps 3 and 4 can be repeated to
draw the morning hour lines. The line OK is drawn, which is parallel
to the 3 p.m. hour line, and the hour lines determined as above.
Another way is to use your compass
to set the distance from point M to the 5 p.m. point on line LM. Move
the compass to point K and mark this distance on line JK. This is the
point for 7 a.m. Repeat this process for 4 p.m. to determine 8 a.m.
This is a very compact method of
drawing a horizontal sundial and it is very easy to draw, for example,
the 6:15 a.m. hour line.