Name______________________ Grade_________________
This assignment is DUE on October 7. Late work
will result in points off.
Read and sign the Policy on Collaboration.
You must attach a copy of this statement with your assignment.
The purpose of this project is to construct and use a simple sundial,
determining and applying all needed corrections to obtain the
correct zone time. The first thing to do is to construct your
sundial using the patterns and instructions that are attached.
Then make your observations as follows:
1. Find the latitude and longitude of your location (to within
1 degree or better) using a map. Latitude = _____________________
Longitude = _____________________. Be sure your sundial is correctly
set for your latitude.
2. Place the sundial outdoors in the sunshine (or indoors if there
is a window which gets a clear view of the Sun). It must be placed
on a level spot. The gnomon (straw) must point towards
true North. True North can be determined in several ways:
(1) You may use a magnetic compass, but be sure to apply the correction
for the deviation between magnetic and true North. This is shown
on many maps, particularly topographical maps, and an outdoors
store in your area is sure to know the value. In Austin, a magnetic
compass points about 7 degrees East of true North. (2)
You can note the direction to the North Star at night, laying
out a line in chalk or otherwise recording the correct direction.
(3) You can use a street map that is marked with a compass to
determine true North. Lay the map out so that the street marked
on the map is parallel to the actual street, and set the sundial
so that the gnomon points to North as marked on the map. (4) You
can use observations of the Sun itself to pin down true North.
When the shadow cast by a vertical object onto a level surface
is the shortest, the Sun is due South, and the shadow of the object
points North.
3. Once the sundial has been set up correctly, you can read the
time directly off of the scale. This is the apparent solar
time. Record the apparent solar time of your observation as
accurately as you can: _____________________. At the same time,
record your zone time as measured by an accurate watch or clock:
_____________________.
4. A correction is needed to account for the varying speed of
the Sun against the stellar background. This correction is known
as the Equation of Time, and there is a graph of it on this handout.
It depends on the date of the year. What is the date on which
you made your observations?_____________________. What is the
equation of time on that date (to the nearest minute)? _____________________.
Should the correction be added to the sundial time or subtracted
from it to get the mean solar time?_____________________. (Hint:
If it is "Sun Fast" then the sundial time will be ahead
of mean time. If it is "Sun Slow", then sundial time
will be behind.) What is the mean solar time? _____________________.
5. If you are not located in the exact center of your time zone,
you will have to make a longitude correction. Time zones
in the US are centered at 75, 90, 105 and 120 degrees. How far
apart (in degrees) are the centers of the time zones? ___________.
If each time zone corresponds to 60 minutes of time, how many
minutes of time corresponds to 1 degree?___________. How many
degrees from the center of your time zone is your location?___________.
To how many minutes does this correspond? ___________. Are you
East or West of the center? ___________. Should you add or subtract
this number to correct the mean time and obtain standard time?
___________. What is the standard time? _________________.
6. Is Daylight Savings Time is in effect?___________. What amount
of time should be added to or subtracted from the standard time
to obtain zone time (as you would read it off of a watch or clock)?
_____________________ should be added/subtracted (circle one).
What is the zone time of your observation? _____________________.
7. It would be very surprising indeed if you got exact agreement
between the zone time, as derived from the sundial, and the time
you read off your watch. How good were your final results? Were
they as good as you expected? List what were, in your opinion,
the main sources of error in this observation in order of decreasing
importance, and explain how big an effect each source of error
might have on the final results. Do these sources of error fully
explain the difference between the time you derived from the sundial
and the time from your watch, in your opinion?
Cut out the three patterns and glue the base and south face to
a piece of poster board. Do not glue the north face yet.
After the glue dries, carefully cut out the base and the south
face. Carefully align the north face and glue it to the back side
of the board on which the south face is glued.
After the glue has dried again, use a sharp pencil or similar
object to punch a hole the size of a straw through the south and
north faces at the center of the dial. Fold the flap on the south
face away from you and glue it onto the base, carefully
aligning the fold along the line, as shown. Note that the glue
goes on the flap that is on the south face of the dial. You may
also use staples if you wish.
Insert the straw through the hole and staple the end to the base
at the indicated place. Adjust the angle of the clock face until
it is perpendicular to the straw. You may use a bit of glue to
fix the straw in position.
