ARCturus

A sundial is a simple device which uses sunlight in the daytime to show time. There are many kinds of sundials, maybe as many as there are inventors. The basic idea in a sundial is that a thin or a little thicker stick fixed on a base produces a shadow, the tip of which shows the time on a scale drawn on the base. In addition to the aesthetic outlook of the sundial, there are many things that need to be taken into consideration when planning a sundial in a public place. The picture introduces a self-made sundial, prepared according to a traditional model (picture IH, Finland).

 

Aim: To prepare a simple sundial by using cheap materials. To test how it works in the sunlight out in nature.

Explorations: It is easy to observe the motion of the Sun with the students either in a classroom or out in the schoolyard. Students are asked to pick an object that creates a shadow and observe the motion of the shadow. Discuss their observations. Try to find a connection between the motion of the shadow and the time it takes. The students can make tentative measurements of the motions a few times at equal intervals.

After the connection between the time and the motion of the shadow has been found with the help of the teacher, it is possible to make plans for preparing a sundial using literature as source material. Let the students in teams bring forth ideas of implementation of the project and models of a sundial. There are many problems that need to be solved before the implementation. For instance, we need to ask the following questions: How to take the latitude into account? What materials should be used? What would be the best size for the sundial in its supposed surroundings? Does the sundial show the current time as it should? A sundial that is meant to be used in teaching can simply be made of a cardboard and a stick. In this case the most important thing is that the tool works properly and supports the understanding of this phenomenon.

1)  Get to know the apparent motion of the Sun that can be seen by means of a stick fixed in the schoolyard. One part of the group keeps track of the time by using a watch and announces the moments at agreed intervals to the others. At those moments the other part of the group marks on the ground the tip position of a shadow produced by the stick. The marks can be either stones or made by using a stick. Discuss the result with the group. This exploration can also be implemented in teams or small groups in the classroom with the help of a cardboard and a stick. Finally, compare the results of the groups and discuss possible differences.

2)  Get to know the basic principle of an equatorial sundial with the help of a mini model. In teams, prepare in the classroom the same kind of a sundial remembering the latitude of the home city. Draw a scale with an hour as a unit on a semi-circle cardboard. Divide the area into 12 parts at intervals of 15 degrees. Fix a stick, i.e. gnomon, indicating the Earth’s axis in the centre of the circle so that the angle between the stick and the base equals the latitude of the city. Test the sundial in the sunlight. Discuss the functionality of the sundial at various times of the day. In the picture, there is a sundial that can be used at the latitude of 60 degrees (picture IH, Finland).

 

 

 

3) Ponder with the students the possibility to construct a big sundial outdoors. Try to find an appropriate peaceful place; ponder the model of the sundial and the construction process. The students can try to find on the Internet sundial models or produce ideas for a sundial of their own. Several important issues must be taken into account when planning the sundial. For example, those are: Does the sundial endure the weather conditions? Is the location of the sundial safe? Is the sundial pretty? Does it give a clear message of the time? Everybody can participate in preparing the sundial if all activities are distributed to the teams. The sundial project can also be a project for a small group as a part of a larger entity.

4) * With the students, find on the Internet educational and artistic sundials. There are gorgeous big and small sundials in ancient historical places. Some of them are in the middle of a park like statues; some have been fixed on the wall or on the roof of a museum or an observatory. If it is possible, take the students on an excursion to some of these places.

5) * An ordinary sundial works during the light hours of the day. Discuss with the students the special cases, e.g. when the Sun shines through the night in the north. Ponder how a sundial in that case could be constructed and how it would work.

6) * Ponder with the students the implementation of a sundial at various latitudes, starting from the equator and ending at the poles. Recognize the special cases like equator, tropics, polar night (i.e. kaamos), midnight sun and equinoxes. These cases can perhaps be illustrated by using the styrox ball and sticks for shadows.

 

Methods: Observing the apparent motions of the Sun in nature, making notes of the locations of the shadows, constructing a sundial as a scale model or a larger version outdoors.

 

 

Materials: Cardboard, cloth, thin and thicker sticks, watch, device for measuring angles, styrox balls.

 

Pondering: Taking the environmental factors into account when making plans for a sundial outdoors, sketching a sundial for night, the moments of sunrise and sunset in the sundial.

 

Evaluation of results: The comparison between the scale models is a necessary and enjoyable activity. The students can decorate their models according to their own inspiration. The most important thing is to ensure that the model works properly.

 

Hints: Many students find it difficult to construct the supporting triangle beneath the face of the sundial. That is because the radius of the face disk, in relation to the triangle’s vertical cathetus fixed in the face disk, must be taken into account. It is worthwhile to first use a sticker before gluing. Adjustments are likely inevitable.

 

Keywords: Sundial, flat sundial, latitude, gnomon, equatorial sundial.

 

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