ARCturus

The planets are celestial bodies orbiting suns. They were born from a thickening cloud at the same time as their sun, as if of extra matter. The circumstances where the planets in the solar systems were born vary a lot. The planets in our own solar system do not resemble each other; most likely neither do the planets in other solar systems. As to their size, two main groups can be formed: planets like the Earth and giant planets. Planets like the Earth, called terrestrial planets, have a solid surface and they are small. The surface of the giant planets is gas or liquid. Their diametre is manifold compared to the diametres of the terrestrial planets. Planets can also have satellites. In the picture, there is a planet system painted on the wall in the corridor of the school (picture IH, Finland).

 

Aim: To get to know the origin and substance of a planet. To practice observing the planets outdoors. To compare the characteristics of the planets in our solar system with each other. To find information on the planets of other solar systems.

 

Explorations: Use the literature and the Internet to find information on the early phases of a star and a probable group of planets around it. Discuss the structure of the solar system, the distribution of matter as well as the motions of all parts of the solar system. The names of the most familiar objects in our solar system are recalled and tested.

 

After this we concentrate on exploring only the planets. The first five planets from the Sun: Mercury, Venus, Mars, Jupiter and Saturn, can be seen from the Earth and they were known as early as antiquity.  The astronomers observed their motions and made notes of their positions against the stars. Especially Venus, the bright morning and evening star, is illustrated in many drawings and paintings on the cliffs. The bright Jupiter has also been an easy object for observation to everyone. Uranus, Neptune and Pluto were only found after the telescope was invented.

 

1) At first we learn to recognize all planets in correct order. Remind the students of the fate of Pluto: since a few years it has only been regarded as a dwarf planet. We also try to remember the symbols of the planets as well as the amount of their moons. A list can be made of their names.

 

2) Explore a table of the planets and try to find differences and similarities between some variables. The most usual variables are diametre, distance from the Sun, revolving period and rotation time. Deepen the understanding on the concepts terrestrial planet and giant planet. Discuss the inclination, i.e. tilting of each planet’s axis, and exceptions to the motions of the planets, like a reverse rotation direction.

 

3) The students are divided into small groups and each group will be given one planet for further exploration. The team figures out the structure of the planet on the surface and in the core by using source material. At the same time we ponder the meaning of the planet’s colour: what kind of material elements it could consist of. Based on the results, a picture as real as possible can be drawn on the wall of the classroom.

 

4) * Explore the distances between the planets and the Sun by using the source material. Test the mathematical expression developed for calculating distances. It is known by the name Titius-Boden law. In the formula a= 0,4 + 0,3 x 2ⁿ the value for variable n for Venus is 0, for Earth 1, for Mars 2 etc. The value of 2ⁿ for Mercury must be 0. It is surprising that there may have been a planet between Mars and Jupiter. Now there is an asteroid belt that consists of small rocks. Therefore the n-value for Jupiter is 4. In literature one can find tables which show that the values for distances calculated by this formula are quite well in accordance with the real values.

 

5) * Choose two planets, the orbits of which are not alike. Calculate on the basis of eccentricity the elliptical diametres of the planets.  Draw the orbits in the same picture by using a pencil and a cord loop. Discuss the shapes of the orbits with the students.

 

6) * Choose two or three points on both orbits, the coordinates of which are defined in the coordinate system placed in the picture. Using these coordinates test how the elliptical equation works.

 

Methods: Use literature and Internet to find information on the planets. On the basis of it, create an impression of the nature, location and motions of the planets. Drawings and graphic presentations support the learning process.

 

Materials: Literature, drawing paper, colours, craft materials.

 

Pondering: When drawing the ellipses it is desirable to ponder the meaning of ellipticity for the planet orbiting the Sun. In addition to that we can discuss how the Earth’s orbit, only slightly elliptic, effects on the circumstances on Earth. A complex topic to ponder is also the mutual impact of the planets on each other’s orbits.

 

Evaluation of the results: The facts about the planets found in literature are well-known and carefully rechecked. They need not be questioned in the classroom. The ellipticity of the orbits is a topic that should be thoroughly examined and further discussed. If for instance the difference between the ellipticity of Earth’s orbit and a circle is extremely small, is there any reason to take it into account? Does it have any effect at all on the existence of our planet?

 

Hints: Drawing the ellipse is both funny and educational. This is also a good opportunity to recall the mathematical secrets of the ellipse and by doing so to support the teaching of mathematics.

 

Key words: Planet, orbit, revolving time, rotation time, inclination, elliptic orbit, moon.

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