The sundial was used as a device for telling time long before the invention of clocks. The sundial uses a an object in the center called a gnomon (NO-mon) to cast a shadow. The shadow travels in the clockwise direction across the sundial as the Sun travels across the sky daily.
There are two important properties of the sundial.
For the K-4 level, we will not worry ourselves about fine tuning the sundial. A pattern for a sundial is provided with this activity so you do not have to figure out the hour angles yourself. The gnomon has an angle of 40° which is right on for central New Jersey. The angles on the dial are set for the same latitude.
Sundials can tell time accurate to within 15 or 20 minutes throughout most of the year. There are some factors that cause variation.
Students can make their sundials and take them outside to tell time. There has to be a way to keep them pointing toward the north. Also, since they are made of paper, they will not last in the weather too long.
It may be possible to make some sundials and keep them taped to a window sill or other location where the Sun can hit them for part of the day. It will be enough to permit the students to see the relationship between the location of the Sun and the shadow that the gnomon makes.
The students can make a sundial and observe it at various times during a sunny day. A Sundial and Gnomon are provided with this activity. Make copies of them for the students to cut out.
1. Students discuss the properties of the sundial and write them in their Science Journals.
2. Students cut out the Sundial and Gnomon from the copies. They glue them on cards. In the figure below, a 3x5 card was used for the gnomon and half of a manila file folder was used for the sundial.
3. The gnomon is attached to the sundial on the XII line as shown in the figure.
The gnomon is attached to the sundial using a piece of plastic tape on each side at the bottom.
4. The sundial is placed with the XII line pointing toward true North. This can be done with a magnetic compass. In New Jersey, the magnetic compass generally points about 11° west of true north which should be taken into account when positioning the sundial.
1. Students have made a sundial which they can use to study how the Sun moves in relation to time.
2. Students can attach the sundial to a board using thumb tacks. They can take it outside and position it correctly. They need to remember that it has to be in a sunny location for most of the day and that the XII line has to point toward true North.
3. Students write observations about their sundial in their Science Journals. If there is a sunny location inside the classroom or the school building the sundial can be positioned there in the morning and the class can come back and check it in the afternoon to see how well it is keeping time.
1. Students research sundials on the Internet. They learn the relationship between the latitude of the sundial on the Earth and the angles of the gnomon and the hour lines.
2. Students research the Analemma. The analemma is the drawing shaped like a figure-eight that appears on many globes. This figure describes the position that the sun will be at noon on any day during the year.
3. Students study the magnetic compass. They learn about it pointing toward the North Magnetic Pole instead of true North. They relate this information to their work in aligning the sundial properly.