ARCturus

Our nearest and most familiar celestial bodies are the Earth, the yellow Moon with its various phases and the Sun shedding light and warmth. Everyone has an opportunity to explore them in an everyday environment. The sunset, appearing different each day, has always a sensitizing and soothing effect on the human mind (picture IH, Finland).

 

Aim: To get acquainted with the characteristics of the three most familiar celestial bodies in everyday life.

Explorations: It is good to start the lesson by a brief recall moment with the students. Discuss with them some basic information on, for instance, what they think is the meaning of the words day and night as well as the question: When can the stars be seen? Also the explorations often begin by getting acquainted with these familiar phenomena in our own neighbourhood and everyday life. Day and night, visibility and motions of the Sun, Moon and the stars belong to everybody’s cognitive sphere. Let’s have a closer look at these phenomena.

1) Explore various cases in a darkened room by using the light of a Sun-lamp. Use a small styrox ball with a wooden stick as an axis to indicate the Earth. Keep the Earth’s axis a little inclined to the same direction and rotate the Earth about its axis.

The Earth rotates about its axis once in 24 hours. Therefore various regions are in sunlight and dark in turn. It is the reason why day turns into night. In The Finnish Science Centre Heureka, there is a photo of the Earth, seen from the space (picture IH, Finland).

 

 

 

2) Use the same equipment and space to explore what happens when the Earth is revolved around the Sun on an elliptic orbit. Use a marker pen to mark on the ball for example Finland and Southern Australia and draw the equator, tropics and polar circles to ease the exploration.

The Earth revolves around the Sun on an orbit slightly elliptic. One revolution takes one year. Due to the elliptic orbit there is once a year one point where the Earth is at its nearest to the Sun and once at its farthest to the Sun. Because the Earth’s axis is inclined at about 23 degrees to the orbit plane, the way the sunlight hits the ground varies during the year. The seasons are the result of this. Especially on the polar regions there is a remarkable diversity in the seasons. For instance, in Finnish Lapland the Sun cannot be seen at all for many weeks in the middle of winter, whereas the Sun in the middle of summer shines all day and night long for many weeks.  

3) Try to illustrate with the same tools the path of the Sun in summer and in winter. In addition to this, sketch these orbits on a paper fixed on a window towards the south. You can do this if the scenery from the window helps you to remember the Sun’s path in the middle of summer as well as in the middle of winter.

In everyday language we say that the Sun rises in the east and sets in the west. This apparent path, ‘motion’, is caused by the rotation of the Earth. In all explorations this concept ‘the Sun’s path’ means precisely this apparent path. The fact is that in our solar system the Sun rotates around its axis but does not move, and the Earth revolves around the Sun. The daily path of the Sun varies during the year. In summer the Sun rises in the northeast, is at noon high in the south and sets in the northwest.  In winter the path of the Sun is a low and short curve, starting from the southeast and reaching not farther than to the southwest.

4) * Explore a scale model, a glass or plastic hood built on a panel, illustrating the path of the Sun (see the next picture and ARC1 Path of the Sun in 24 hours). Inside the hood, on the panel, there is a yard with houses, trees and a garden. Mark a zero point on the yard in the middle of the hood. The rays of the Sun are focused at this point. Fix stickers at the point where the ray intersects the hood. For extra charm colour the stickers to little suns.

Observations can be made, for instance, at one hour’s intervals on various days and during various seasons. On the hood there will be many ‘pictures of suns’. They illustrate the Sun’s daily path which varies according to the seasons. A low curve indicates months of the winter and a high curve the summer months.

5) *Define the declination of the Sun in degrees at its highest and lowest. Use, for example, a stick fixed on the ground and the shadow it produces, or an orbit drawn on paper which is fixed in the window. Also an astrolabe can be used (see ARC1 Astrolabe).

Methods: Using balls in various sizes illustrate the motions of these three celestial bodies in relation to each other. A lamp (the Sun) demonstrates how the sunlight hits the Earth and the Moon. The path of the Sun in its various phases can be seen on the hood. A trigonometric measurement method is used to define the declination of the Sun.

Materials: Plastic or styrox balls in various sizes, long and short wooden sticks, lamp, colouring pencils or marker pens, darkened space, hood, stickers.

 

Pondering: How do the Finnish day and night differ from the Australian day and night in the middle of summer? What kind of a daily path does the Sun seem to have in Finland and Australia?

Evaluation of the results: The results of exploration can be dealt with in many ways. For instance, they can be discussed together or the phenomenon can be opened to the other students in the classroom by letting the exploration team process it to a model. The students or the teams can also be asked to draw their observations or prepare together a poster on the observations of each team.

Hints: The groups should be small and sufficiently separated from each other during the explorations in a darkened room in order to prevent the light of a lamp from disturbing the observation of the other group.

Keywords: Day, night, day and night, season, orbit of the Earth, declination.

 

 

 

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