Make a Horizontal Sundial  Graphical Method
3
Horizontal Sundial: the common or
garden sundial with a horizontal dial plate and polarpointing
gnomon.
Here is yet 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
are combined. Step
1

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.
Step
2

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.
Step
3

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
horizontal line.

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
OC.
Step
4

Extend the horizontal lines CK and
CM to points F and G where the distances CF and CG are equal to the
distance CE.

Draw a circle with centre F and
radius OE.

Draw lines on either side of FK
spaced at
15° intervals. If you want smaller time intervals
add more lines.

Extend these lines to the line JK.

Extend the line JK to the point R
so all the hour points are on the line JKR.

Draw a circle with centre G and
radius OE.

Draw lines on either side of GM
spaced at
15° intervals. If you want smaller time intervals
add more lines.

Extend these lines to the line LM.

Extend the line LM to the point S
so all the hour points are on the line LMS.
Step
5
Step
6
This is a very interesting method of
drawing a horizontal sundial and it is very easy to draw, for example, the
6:15 a.m. hour line.
Happy Dialling!
