Students will need a working vocabulary of terms, and a basic understanding of what an eclipse is and how it occurs. Initial lessons will explain how an eclipse occurs with subsequent lessons instructing students to create a model of this phenomena. For our purposes, and our calculations, we will consider the earth the center of our system (the Ptolemian system as opposed to the Copernican system). We will use this system only as a means of explanation. Hopefully students understand that the sun is the center of our solar system with the earth orbiting the sun and the moon orbiting the earth. The moon completes its trip around the earth in one month while the earth completes its trip around the sun in one year. Occasionally the sun and moon cross in front of one another. When the moon passes between the sun and the earth so as to block the sun from sight, a solar eclipse occurs, the moon’s shadow blocking out the sun’s rays. The moon blocks a portion of the sun’s rays causing a dark “spot” on the earth’s surface. People living in the region can observe, with necessary precautions, the moon passing in front of the sun with darkness following in its wake and the eventual passage of the moon with the return of light. (Figure I) Similarly, when the sun and moon are at opposite sides of the earth, i.e. the sun and moon are in opposition (180° apart), a lunar eclipse occurs. Essentially the sun illuminates one side of the earth causing daylight while the opposite side of the earth remains dark. The opposite or night side of the earth casts a shadow, called the umbra. A lunar eclipse occurs when the moon passes through this shadow of the earth blocking it from the sun’s illuminating light and consequently from sight. The moon itself casts no light and is dependent upon the sun’s rays for its illumination. When the moon passes through the shadow, sun rays its source of light, are blocked and the moon can not be seen.
(figure available in print form)
Lessons explaining the movement of the sun and moon should insure the students’ understanding of what is physically happening when an eclipse occurs. Students can draw diagrams or construct models using light bulbs and Styrofoam balls to show the sun and moon at opposition. Also many school science laboratories have modelsof the earth, sun, and moon that can be used to illustrate an eclipse.
The first week of the unit should concentrate on students understanding the scientific explanation of an eclipse. Students should not begin the computational work until they have a viable working image of the physical occurrences during eclipses. In addition to a working Knowledge of the occurrence, a list of working definitions should be introduced and reinforced throughout the unit. The basic terms, some of which have been introduced and those that will be introduced are listed below. Definitions and explanations will follow.
Vocabulary Terms
:
|
1. Longitude
|
6) Greenwich Hour Angle
|
|
2. Latitude
|
7) Greenwich Mean Time
|
|
3. Eclipse
|
|
8) Prime MeridianCelestial Meridian
|
|
4. Opposition
|
9) EquatorCelestial Equator
|
5. Declination
