ARCturus

Our solar system belongs to a huge collection of stars, the Milky Way. It is a flat spiral galaxy with many hundreds of billions of stars, thicker in the centre and thinner at the outer parts. Its spiral arms are evenly distributed. The neighbouring galaxy, Andromeda, resembles our Milky Way. Observing and exploring it has given us valuable information on the structure of the Milky Way. When the sky is dark and clear, the Milky Way reaches like a light zone across the sky (picture from The Star Maps).

 

Aim: Get to know the structure and dimensions of the Milky Way.

 

Explorations: Discuss with the students the structure of the universe and constellations in general. Take a brief look at the various types of galaxies and then choose our own galaxy, the Milky Way, for the object of further exploration.

 

Get acquainted with the characteristics of the Milky Way by using source material. The Milky Way is a flat disk with spiral arms curving from the bulge in the centre. The bulge consists of billions of stars, whereas their amount in the spiral arms is not so huge. The diametre of the galaxy is 100 000 light years and the thickness of the bulge about 10 000 light years.

 

Our solar system is situated in one of the spirals at the distance of 25000 light years from the galactic centre. Our Sun and the nearest stars revolve around the Milky Way centre once in 250 million years. The total mass of the Milky Way is estimated to equal the mass of over one thousand billion Suns. According to the most recent scientific understanding it is assumed that in the centre of the Milky Way there is a black hole, the size being as huge as the mass of one million Suns. On both sides of the galactic disk there are spherical clusters of stars.

 

1)  Sketch pictures of the Milky Way on paper both face-on and sideways. Use a scale that fits to the paper size. Mark the Sun’s position in the picture.

 

2)  Use craft materials to prepare a mini-size model of the Milky Way. First, draw the outlines of a spiral galaxy seen face-on upon a stiff cardboard and cut it loose. Use paper mass or cotton wool to prepare a bulge to the galaxy in a correct scale. The spiral arms may be prepared of the same material and glued on both sides of the cardboard. They are made thicker at the bulge and become thinner at the other end.

 

A yellow self-made paper mass ball or a prefabricated ball, indicating the Sun, is fixed in a correct position in the spiral arm. Mass or pearls may be used to prepare spherical clusters of stars. Under the disk they can hang on yarn. Fixing them on the upper side needs a stiff metal thread. The students can paint the model as they please.

 

3)  A mini-size model can be prepared in teams or as a common project for the class. With the finished models at hand discuss how illustrative they are. Ponder together how the model could be improved. Ask the students to innovate new kinds of model implementations.

 

4) * Use the Internet to find information on other kinds of spiral galaxies. Note the amount and shape of the spiral arms. Find a more precise definition for the concepts “regular and irregular spiral galaxy”.

 

Methods: Preparing a mini-size model of a galaxy and illustrating its motions. Exploring the distribution of matter.

 

Materials: Cardboard, craft cotton wool, balls, colours.

 

Pondering: It is worthwhile to use the pictures of galaxies to exploring the amount of spiral arms. Are they positioned in pairs on the opposite sides of the galaxy? Is their length the same?

 

Evaluation of the results: Compare the mini models in case there is more than one and discuss possible biases. Ponder how it would be possible to illustrate the black hole in the centre of the galaxy. Ask the students to comment on the colours used.

 

Hints: Instead of using cardboard, the disk can be made of paper mass and glue. Preventing the mass from breaking down may need a wire net or wires inside the mass.

 

Keywords: Galaxy, spiral arm, spiral galaxy, light year, cluster of stars, black hole.

 

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