ARCturus

When the Earth revolves around the Sun, it seems as if the Sun’s path always goes via the same constellations. For instance, during the summer solstice the Sun is in the tropic of Cancer and during the winter solstice in the tropic of Capricorn. This apparent path of the Sun via constellations is called ecliptic and the chain of constellations the Zodiac. The Sun’s path goes through 13 constellations, but usually only 12 of them are included because the year is divided into 12 months. The constellation Ophiuchus is not usually mentioned when speaking of the Zodiac. In the picture, the participants of the astronomy course (in Tavira, Portugal, see The Organizations/EAAE) create ‘a living model’ of the Zodiac. Each one introduces one constellation in the Zodiac. The bright lamp in the middle indicates the Sun and the globe the Earth (picture IH, Finland).

 

Aim: Get to know the position of the Sun during various seasons. Explore the Sun’s apparent path in the sky during the annual revolution of the Earth around the Sun. Prepare a mini-sized model.

Explorations: An ordinary bulb may indicate the Sun and a styrox ball the Earth. Push a stick through the styrox to indicate the axis of the Earth. Use a marker pen to draw the equator. Students’ desks may show the orbit level of the Earth in the classroom.

1) Use star maps and explore first constellations along the Sun’s path, i.e. the ecliptic, and make a list of them in correct order. Recalling the astrological signs in correct order helps in picking them up.

2) The pictures of the ecliptic constellations can be found in literature; copy them on film. Use an overhead projector to project the picture of the constellation from the film to an A3-size paper on the wall. Working in teams, make the students draw, each in turn, the symbols of the brightest stars in the constellations on paper and colour them if they want. The mythological figures of the constellations bring extra colours to the poster. Pictures of them can also be found in literature (i.e. Lovi, G., Tirion, W. 1973. Men,monsters and the modern universe. USA: Willmann-Bell, Inc.) The students use their imagination to colour the human and animal symbols (picture IH, Finland).

 

 

 

 

 

3) When the introductory phase is finished, a decision needs to be made on the position of each constellation of the Zodiac around the Earth-Sun-setup in the middle of the classroom. The rule to follow is: each sign of the Zodiac is at hand when the Sun is – seen on the Earth – in that constellation. For instance, at the end of November the Sun’s path goes via the constellation Sagittarius, i.e. seen on the Earth. The constellation seems to be behind the Sun. (It is not allowed to look straight to the sun with the naked eye!) When positioning the constellations, it is worthwhile to start from the equinoxes and solstices. At each of the four, the Sun is in a certain constellation. After that it is easy to position the rest – 8 constellations – in correct order in four quarters between them.

4) It must be kept in mind that the ecliptic deviates 23 degrees from the orbit level of the Earth. This has to be taken into account by positioning one solstice above ‘the desk level’ and the other below it. The equinoxes are, of course, on the level of the desk surface, i.e. that is called a knot spot. Each student may have a constellation of his own to present. Students can make an illustrative performance and create a charming ‘living model’ of the Zodiac.

5) * There are many ways to make the model more detailed. When exploring the star maps it is easy to notice that the position of a constellation is not always exactly and evenly behind the ecliptic. In some constellations the major part of the stars is on the northern side and in some others on the southern side of the ecliptic. The size of the area the constellation takes varies. The students can explore these phenomena and define the model accordingly. It is good to discuss with the students the positions of the Earth and the Sun. For instance, does the ellipticity of the orbit have a significant impact on the model built?

6) * With the model at hand, it is very interesting to ponder the essence and meaning of the mythological figures to the people of old times. Comparison between the modern and old times is certainly an inspiring topic, even to the students. It is interesting to explore how differently the ancient peoples of the world see and interpret the messages of the constellations and various star figures. These explorations may be carried out in teams or as projects of the whole class.

Methods: Find the constellations of the Zodiac in the star maps and introduce their major stars in a chosen scale on A3-paper. Arrange the pictures according to the Sun’s apparent path in a suitable space. Discuss the following topics: illustration of the inclination between the ecliptic and equator level, positioning the pictures of the constellations in the scale model and the meaning of equinoxes and solstices.

 

Materials: Lamp, styrox ball, long sticks, A3-size paper, marker pens, overhead projector, literature.

 

Pondering: Discussion with the model at hand is very important. This is the way the teacher can make sure that the students have a clear and correct picture of how the model projects the huge universe and illustrates the meaning of the equinoxes and solstices. In addition to this, ponder what it would mean if there were no inclination between the ecliptic and the equator level.

 

Evaluation of the results: The students can bring forth their own interpretations of how good they think the model is and how well it works as it should. Possible biases should also be discussed. With the model at hand, encourage the students to ask ’what if’questions and find together answers that would be correct and possible. The imagination of the students may create new innovations of the world!

Hints: The teacher evaluates the exploration project with the educational level of the student in mind. The emphasis should be on the student’s commitment, diligence and willingness to produce new ideas. If needed, the teacher can help in finding valid information. Students must be required to reach an adequate level of know-how.

The student should be required to ensure that the projection of the reality the model presents is as good as it possibly can be. On the other hand, it is worthwhile to discuss, with the model at hand, possible biases and misunderstandings. It is easy to find illustrative material in literature for the exploration project.

Keywords: Zodiac, ecliptic, orbit level of the Earth, knot spot, solstice, equinox, vernal equinox.

 

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