Exploring Galileo's Telescope
Straulino, Samuele, Terzuoli, Alessandra, Science Scope
In the first months of 2009, the international Year of Astronomy, we developed an educational project for middle-level students connected with the first astronomical discoveries that Galileo Galilei (1564-1642) made 400 years ago. The project included the construction of a basic telescope and the observation of the Moon. The project, if completed in full, can be accomplished in about 20 hours over the course of a month.
The experimental method and an introduction to Galileo
During the first lesson we gave each student a lab notebook to use throughout the project for recording observations, doing homework assignments, and completing in-class activities. During this first lesson we asked students to write in their notebooks five words they associate with scientists and their work, such as study, observe, analyze, experiment, discover, and invent. Students then read their words aloud and the teacher recorded them on the blackboard. We then discussed what scientists do and how they might approach a subject they are interested in studying. Finally, guided by the teachers, students discussed the processes of science.
During the second lesson, students were introduced via a computer presentation to the most important scientist for our project: Galileo. The presentation included information about when Galileo lived, his studies, his career, the centrality of the experimental method in his research, his inventions, the telescope, the major astronomical discoveries he made, the geocentric versus the Copernican system, and why Galileo was put on trial for his ideas. There were images of paintings from this period, pictures of instruments, planets of the solar system, and the beautiful drawings that the scientist himself created to document his observations of the Moon. Information and images are easily available on the internet; teachers can choose what to use according to their preferences, or instead of presenting the information ask students to research aspects of Galileo's life and times and share their findings with the class. This study of Galileo was continued in a history class where students learned the historical relevance of this scientist.
[FIGURE 1 OMITTED]
First observations about light
After the introductory lessons we shared with students some basic, grade-level-appropriate information about the behavior of light:
* Light moves, starting from a source and reaching an object.
* Light moves very fast; only when the light source is very far from us (e.g., the stars) does light take a long time to arrive.
* Every illuminated object diffuses light around it; when this light enters the eye, you can see the object.
* Light moves along straight lines, as shadows might indicate.
* Sunlight is composed of several colors; with a prism or a glass crystal it is possible to separate the colors of the light.
* An object can absorb or diffuse a sunlight color. The eye can see only the diffused color, which is responsible for the "color" of the object.
* A lens can make light rays approach or separate; lenses can be converging or diverging. Different lenses are used in everyday life, such as magnifying glasses and eyeglasses.
We discussed the first three points with students, and they verified the other points using simple materials and everyday objects. For example, to understand that light moves along straight lines, students observed the geometrical relationship between the shadow produced by an object and the object itself. Some crystals taken from a chandelier were useful to show the separation of the colors (see Figure 1); working in pairs, students observed the phenomenon with a flashlight in the darkened classroom or using the direct sunlight entering from the window. Then they recorded their observations in their lab notebook.
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A glass of water was used as a converging lens to show that the dimensions of a vertical pencil immersed in water appear different depending on the pencil's position in the glass. …