The Earth/Sun/Moon System

Investigations for Third Grade

Introduction

The following is a set of suggested activities for a third grade curriculum unit on the Earth/Sun/Moon system. The goal is to provide students with an understanding of the motions of the three objects in the system and the way in which they determine the periodic changes we observe. In particular, students should develop an understanding of the way the Earth's daily rotation determines the cycle of light and dark that we call day and night; the way the Moon's motion about Earth determines the monthly cycle of lunar phases; and the way the Earth's orbital motion around the Sun determines the annual cycle of seasons. We also discuss how eclipses – solar as well as lunar – come about.

The cyclic changes we discuss are a visible and essential part of students' experience. In finding that they can systematically state, quantify, and model these changes, and that they can furthermore comprehend the astronomical phenomena that underlie them, students acquire not only a familiarity with scientific methods and facts but also a sense that these methods render the physical universe they inhabit essentially comprehensible. This in itself is an important aspect of teaching the unit, and we have attempted to structure the activities to make it explicit.

The activities are constructed to fulfill the requirements of the North Carolina Standard Course of Study objectives for third grade science. Included in these is an understanding of some aspects of the nature of Light. Several of the activities address this – they occur early in the Unit, as the facts about light are used extensively in the following Activities. As a study of light this is woefully incomplete; some related enrichment activities are included for teachers interested in taking this to slightly greater depth.

The understanding we aspire to make available to students involves thinking about the motions of the bodies in the system in three-dimensional space and can be quite challenging. The essential tool for making the abstract ideas comprehensible is the gradual construction of a model of the system which the students manipulate and observe in the classroom. In our model, a bright light bulb located in the center of the classroom will represent the Sun, a large (4” diameter) styrofoam ball the Earth, and a smaller (2” diameter) styrofoam ball the Moon. The classroom itself, with its walls, desks, and students, will become outer space, the dark vacuum in which these bodies exist; objects in the classroom, which remain fixed as we manipulate the “Earth” and “Moon” will be used to represent distant stars which appear fixed in space as the Earth and Moon move. The students themselves, inhabiting this region of space, will become “space giants,” far larger than “Earth” and capable of surviving in space. The transition from the classroom as classroom to the classroom as space will be signalled by extinguishing the lights, and often by turning on the “Sun.” While simplified and certainly not to scale, the model will capture most of the essential aspects of the phenomena we study. Manipulating concrete objects harnesses the student's intuition and observational skills. In fact, many of the complex concepts become “obvious.”

The challenge, then, is to help the students translate phenomena as they are observed by the “space giants” to the experience of Earth-bound beings. This translation between the two different points of view will be gradually developed and is one of the important threads through the latter Activities.

Some of the concepts with which students are presented in this Unit are quite complex. It is unreasonable to expect that all students will grasp these at the same depth. Students emerging with an incomplete grasp of the concepts, however, will still benefit from the exposure. Studies show that many educated adults suffer from deep misconceptions about the nature of the phenomena we study, and many of these misconceptions are inculcated early. Encountering correct scientific explanations, as well as the scientific method of addressing questions, at a young age is an important antidote to these, and students will be more prepared to encounter the issues in higher grades (in North Carolina, much of this is reviewed in 6^th grade).

The material in this unit and the teaching methods employed may be unfamiliar. DON'T PANIC. Teachers report that initially difficult concepts are far more clear to them in their second year with this curriculum, and the teaching methods second nature. Most of the learning in this unit will be through observation and active manipulation of models. We encourage you, the teacher, to help them collect their observations, generalize them, and ensure that the connections to the real-world phenomena are clear to all of them. This can be done through class discussion, questions and answers, demonstrations, etc. following the interactive Activity.

One important aspect of these notes is that we have made every effort to structure them so that students have an opportunity to observe in Nature as many of the phenomena under investigation as is possible. The challenge here is that some of these, like seasonal changes, can only be observed by making observations in different seasons – requiring that the teaching of this unit be distributed over essentially the entire school year. The activities described here are an attempt to combine the temporal requirements of observation with a sound pedagogical development of the material.

In teaching students these subjects it is natural that many questions will arise that are not addressed here, but would be natural extensions of the material included here. Examples of this are the nature and structure of the Sun and the Moon, their history and origin, the story of human exploration of space in general and the Moon in particular, etc. We have included some fragments of such information in the Teacher Background sections of the units but teachers should expect many relevant questions not answered here to come up. We plan to include an indexed database of some of these questions, together with the beginnings of answers, on this site. Please forward questions your students come up with to plesser@cgtp.duke.edu and we will try to respond by email, as well as collecting questions and answers for our database.

Finally, we have found that teaching this unit has been significantly enhanced by field trips to the Duke Observatory to observe some of the concepts in the sky. See http://www.cgtp.duke.edu/~plesser/observatory/ for details. If observatory visits are not practical, we strongly recommend an evening meeting for naked-eye observing to render abstract concepts concrete.

The curriculum materials presented here were produced by J. Heffernan and R. Plesser. They are based on material developed by Ronen and presented at Forest View Elementary in Durham, NC by Ronen and by students from Duke University, and were first written up by John in the summer of 2003, with support from the NASA Space Grant program. This version was supported by a Kenan Fellowship. We thank many teachers and students who, in using the materials, helped us understand where more work was needed. Particular thanks go to Lisa Byrd and Rhonda Swaringen, who helped produce a previous version for the Durham Public Schools.

Outline

The unit includes a set of interactive, hands-on Activities. We begin in “The Sun Moves in the Sky” by tracking the motion of the Sun in the sky over the course of a day. The first part of the unit is devoted to developing an understanding of the causes and implications of this cyclic motion; in this Activity, however, we make no attempt to go beyond a careful, detailed observation of the pattern itself. Since the Sun's path changes with seasons, reflecting the tilt of Earth's axis, we recommend that this Activity be repeated three times during the course of the year, in fall, winter, and spring.

To understand how the daily cycle of light and darkness is driven by the Earth's rotation, a few fundamental properties of light must be clear to students, and the next two Activities – “Light and Darkness in Space” and “Pinhole Viewers” are designed to help students understand light as a form of energy that moves in straight lines.

Building on this understanding, students next track the change in their shadows over the course of a day, paralleling their study of the Sun's path earlier, in “Shadow Tracing.” This reinforces and recalls the patterns established in the first Activity. It also sets up an important property of shadows. When we work with models, we will not be able to directly observe the world from the point of view of a model “person” living on our model “Earth.” We will, however, be able to see the “person's” shadow. We first try this out with a plate serving to model the ground we stand on, and a vertical straw “person” modeling our “person” in “As the Plate Tilts.” Students will recreate the pattern of changes of their shadow over the course of a day by moving the plate in the presence of a fixed light source modeling the Sun. Reproducing the sequence of morning, noon, and evening shadows by rotating a plate models the effects of Earth's daily rotation. In the next two Activities, “What's Up, Earth” and “Spinning into Darkness, Spinning into Light,” students will use styrofoam model Earth's to investigate how the insights from rotating plates transfer to a spherical planet.

Having rather thoroughly studied and explicated the daily cycle of light and darkness, the next two Activities, “Your World is Tilted” and “Seasons and the Orbit” investigate how the fact that the Earth's axis is tilted relative to its orbital plane causes the annual cycle of seasons in the two hemispheres. In the first of these, the effects of a tilted axis will be investigated and students will see that this causes the length of days and nights to vary with latitude, longer days in one hemisphere being related to longer nights in the other. In the second, Earth's orbital motion around the Sun, together with the fixed, tilted direction of the axis, will be seen to be the cause of seasonal variations.

The next three Activities, “Phases of the Moon,” “Eclipses,” and “Dance of the Moon and Earth” focus on the monthly cycle of Moon phases. Students first discover how looking from different angles at a round styrofoam “Moon” in the presence of the fixed “Sun” causes the illuminated part of the ball to change shape just as the Moon does. In “Eclipses” they will see how alignment of Sun, Moon, and Earth can lead to lunar and solar eclipses. Finally, in “Dance of the Earth and Moon,” they combine their understanding of the daily and monthly cycles to model both motions. At the end of this Activity they will realize how the Moon's phase is related to the times of day it is to be found in the sky. Sometime before launching into this material, it is recommended that students follow the Moon's shape and location in the sky over at least a month, as described in “Moon Cycle Calendars.”

A final, summary activity, “Dance of the Earth, Sun, and Moon” invites students to combine all three motions in a complete model. At the end of this Activity, students will understand how it makes sense that the Earth's rotation about its axis in fact takes four minutes less than 24 hours.

Additional Activities, extending those listed in various directions, are included separately. These include four additional Activities investigating the nature of light and the production of images: a quantitative study of shadows in “How Long?” offers the opportunity for an extension into the mathematics of similarity, proportionality, and scale. “Mirror Mazes” examines reflections off mirrors in a playful, hands-on way, while “Secret Lenses” shows how images can be created by an edible lens. “Shadows of Time” invites students to extend their investigations of shadows to create a sundial, and “Star Shapes” is an introduction to the night sky and some constellations. Literacy extensions into various mythologies are indicated. We also describe the use of a daily activity with an “Earth Calendar” to amplify and enhance students' comfort with the concepts in the unit.

Technicalities

The materials provided here are not copyright. You are welcome to use them, duplicate, or modify them to suit your needs. To this end, most of the Activities are provided both as Word documents (.doc) and as pdf files (.pdf). The former are quite large, and are recommended only if you wish to make modifications. If you modify the files and do not mind sharing your ideas, please forward them to plesser@cgtp.duke.edu,Thanks! To view or print, the latter are easier, and can be read with free Adobe Reader software. To view files simply click on the links; to download, right-click on the link and select “save target” from the drop-down menu.

We are still compiling the files for this unit, please be patient. As more are completed we will update this page. If you find errors or wish to suggest corrections, please let us know.