Making a Sundial

Marc walked into our bedroom this morning and mentioned how the sunlight plays on the bathroom wall.  He noted how the light gradually slides down the wall as the morning progresses, with it eventually disappearing as the sun rises toward midday.  He thought he could make marks on the wall to indicate the time of day.

We told him that it would be better if he not mark up the bathroom wall; if he really wanted to do this little experiment, we told him to tape paper to the wall and mark the paper instead.  Then we told Marc about sundials, and how they told people the time before the age of watches.  This  piqued his curiosity, and so in a few minutes we were searching the internet for instructions on making a sundial. 

We needed just a few tools to make this temporary sundial:  A ruler, a protractor, a pen, a marker, and a knife.  We decided to make our first sundial out of cardboard.

Here Marc is cutting out the base piece from some leftover cardboard.

 Notice how Marc is always safety conscious....

 Here is the protractor and a sheet of paper we downloaded from the internet with lines already drawn for the hours.

 Here is one of the vital steps to the process.  One must know your location in latitude and longitude.  I always get the two confused, so I have to look it up.  Latitude are the horizontal lines which tell how far you are (in degrees) from the equator.  For our home, we are at 32 degrees North.  This number is used to make the 'gnomon,' or the part of the sundial which casts the shadow.

We traced the protractor onto another piece of cardboard, and then determined a 32 degree angle.  i cut the gnomon out of the cardboard.

 Longitude, by the way, is the distance (in degrees) from a vertical line running through the planet.  By convention, the reference point goes through, Greenwich, near London.

The next step was to mark the hours on the base of the sundial.  We traced them on this piece of cardboard, and Marc labeled the hours from 6 a.m. to 6 p.m.

 Using some strong packing tape, we secured the gnomon onto the base.  We were ready to tell time.

 We place the sundial in the back yard and lined the '12' line up with North on my iPhone compass.  The picture below was taken at about 10:30 a.m.

Hmmmmmm.

What did we do wrong?  After moving the base around, making sure there were no large metal deposits below us, and switching from the 'True North' and 'Magnetic North' settings, I figured it was the Sun's fault.  Maybe it was the Earth's fault.  Global warming certainly had something to do with it.

After a while, I started thinking that the sheet we used to trace the hour lines was from a website based in England.  I suspect I shall have to go online and figure out how to calculate the 'hour' lines for our home in North Texas.  I shall put on an update about this after I investigate it further. 

Still, this was a cool thing to do with the children when I should have been sleeping after a night on call.

The rocks are on it to keep the wind from blowing it away.