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Moon phases

The Moon orbits the Earth and during the period of one month its light reflecting appearance is constantly changing. One orbit takes one month. When orbiting the Earth the Moon rotates around its own axis once in a month. That is why we on Earth always see the same side of the Moon. It also means that 24 hours (day and night) on the Earth lasts one month on the Moon. The orbit level of Moon differs a little from that of the Earth. That is why Moon sometimes is high in the sky and sometimes quite low in the south. The size of the sunlit area seen on the Earth varies regularly. This periodic series is called the phases of the Moon. One of the phases, the half Moon, is seen in the photo below (picture IH, Finland).


Aim: Learn to know the phases of the Moon by exploring the phenomenon in a darkened room by using a lamp and a moon ball. Learn to recognize the phase and location of the Moon by concluding on the basis of information available.


Explorations: The exploration circumstance is similar to the one in the workshop ARCI Earth and Moon. In a darkened classroom a bright lamp indicates the Sun and a small styrox ball the Moon. The head of the explorer is the Earth. It means that his eyes demonstrate the observer on the Earth. Students can make a circle around the Sun. Each one of them can simultaneously have a topic of their own to explore since the directions of real life have no meaning in this.  Every explorer learns how to use virtual orientations by paying no attention to the class and the scenery seen from the windows. The styrox ball demonstrating the Moon may be painted yellow if it helps the imagination. A white ball is as useful as it reflects very well the light of the lamp. Hold the moon ball in your hand or by using a stick and move it around your head. Notice how the size of the light area changes.

1)  Move the moon ball a full circle around the head anticlockwise and observe at the same time the appearance of the  light area. The same circle may be repeated several times in order to make sure that various phases have been noticed. In order to get a correct impression it is necessary always to make the circle anticlockwise. Only then does the proceeding of the phases reflect reality.

2)  Try to draw the previous result on paper as such as it was seen on the Earth. Draw a circle using Earth as a centre, on the circumference of which colour the bright and dark area in small Moon circles according to the observations. In addition to that, draw in the picture another circle with the Earth as centre. Draw the real phases of the Moon on that circle line seen from above the Moon’s orbit plane.

3)  Use the model to identify the special phases of the Moon: New moon, first quarter Moon, Full moon and last quarter Moon. Draw a strip cartoon of them in the correct order. Memorize the English names of these phases. Discuss with the students rare phenomena like the solar and lunar eclipse.

4)  * Students can use this simple and illustrative model to exercise the basics of problem solving. They will be given two variables out of three as preconditions. These variables indicate the phases and orbiting of the Moon. Students’ task is to determine the third variable. Below there are some examples of topics that can be explored:

-  At what time of the day can the first quarter Moon be seen simultaneously with the Sun?

-  At what time of the day can the last quarter Moon be seen simultaneously with the Sun?

-  Where is the Moon at noon if it is starting to wane?

-  What phase of Moon is going on if the Moon is in the southeast when the Sun rises?

-  What is the time of a day if the last quarter Moon is seen in the east?

5) * Explore the appearance of the Moon between special phases. What names could they have? The previous task used the concept ‘starting to wane’. Write down a few possible names for intermediate stages and compare them with the terms mentioned in literature. Discuss with students the well-known term ’crescent moon’.

6) * Use the model and explore more carefully the visibility of the crescent moon at various latitudes. Try to verify the allegation of the tourists that the Moon looks like a boat floating on the celestial sea. In northern latitudes the crescent moon is always a little inclined.

Methods: Explorations are carried out in darkened rooms by using a lamp and a styrox ball. With the model at hand discuss various situations and also demonstrate special occasions. Draw observations into graphs. In addition to these, try to do observation activities out in nature whenever it is possible.

Materials: A bright lamp that sheds light into all directions, small styrox balls, wooden sticks, thick paper.

Pondering: How to help students to perceive virtual orientations? It is useful to practice with the students various kinds of situations in space in order to determine directions.


Evaluation of the results: Comparison between the results drawn on circle lines of two nested circles may turn out surprisingly difficult because of cross observing directions. Many people find it difficult to perceive things spatially. A human mind is so dependent on the stable essence of its surroundings with orientation that it is almost impossible to ignore them and just float in the universe.


Hints: Playing and using games can be a good means to practice understanding of virtual surroundings. If it is too challenging to accept any direction, the model can be set up according to natural orientations. In any case the most important thing is to understand this phenomenon.


Key words: Phases of the Moon, full moon, new moon, crescent moon, Moon’s orbit, solar eclipse, lunar eclipse.


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Seuraava sivu: Shapes of the Moon's surface