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Transcript
Comparison of Common Student Ideas and Scientific Ideas about the Sun, Earth, and Moon for Use in Planning the LSD Grade 5 First-Quarter Science Unit Planning a science unit is much like planning a trip. To select a route for a trip you certainly need to know where you want to go. Similarly, when planning a science unit you need to know where you want your students to be (i.e., what they will know and be able to do) by the end of the unit of study. Clusters of benchmarks from the Michigan Curriculum Framework (2000) for science, as specified by our district’s science pacing guides, define the destinations for our quarterly science units for grades 2 through 5. But selecting the route for a trip also is dependent on where you start. For example, Interstate 96 is a reasonable route to follow if you want to go from Lansing to Grand Rapids. However, if you are starting from Traverse City, Interstate 96 isn’t likely to be part of your journey. Similarly, when planning a science unit, you need to know where your students are when you launch the unit. Depending on past experiences (both in and out of school), students can begin a new unit of study from widely different locations. Fortunately, these starting points are not entirely random or different for every single child. More than three decades of research have indicated that there are some very common and widely shared naïve beliefs that students bring to their study of many science topics. By becoming familiar with these naïve conceptions, we can more easily spot them during pre-assessments and adjust accordingly the route that our unit of study will follow. Listed below are several issues related to our fifth-grade study of the sun, earth, and moon for which research (as reported, for example, in the chapter “The Earth in Space” in the book Making Sense of Secondary Science: Research into Children’s Ideas, edited by Rosalind Driver, et al., 1994, ISBN: 0-415-097657) has found naïve beliefs that are shared among many students. For reference and contrast, statements of corresponding scientific conceptions are included as well. Goal Conceptions or Understandings Issue Earth’s Shape People on the Earth Where Is the Earth? Page 1 of 4 Handout #13 Common Naïve Conceptions or Beliefs The earth is simply a flat surface. The earth is shaped like a flat, round disk (e.g., like a pizza). The earth is a sphere; people live inside the sphere (so they won’t fall off). [Down is conceived of as an absolute direction.] The earth is a sphere; people live only on the top of the sphere (so they won’t fall off). [Down is conceived of as an absolute direction.] There are two earths: the one we live on (which is a flat surface) and the one in the sky that we can see as a tiny sphere of light at night (like any other planet). [NOTE: For the sake of completeness, some of these statements involve facts and understandings that go well beyond what is expected of students in our fifth-grade “Astronomy” unit.] The earth is essentially a large sphere. People live on the outer land surface of the spherical earth. Down is toward the center of the earth. Gravity pulls all objects near or on the earth toward the center of the earth. Earth is the planet on which we live. Naïve & Goal Conceptions for Sun, Earth, and Moon 2001.08.29 [RTSmith] Revised 2002.09.01 What Has Gravity? Animatism Daytime and Nighttime When Is the Moon Visible? Size Page 2 of 4 Handout #13 Only the earth has gravity. The sun, earth, and moon each have gravitational fields, with the sun having the strongest gravitational pull (nearly 28 times that of earth) and the moon having the weakest gravitational pull (about 16% of earth’s) of the three. [Actually, all “masses” – not just the sun, earth, and moon – have gravity.] The sun and/or the moon are The sun, earth, and moon are all inanimate animate; they can have and act on objects. intentions, often treating each other as companions or as antagonists. Daytime and night result from The sun gives off light in all directions. active/animate/intentional actions The side of the earth that faces the sun is of the sun and/or the moon. illuminated; this is daytime. The side of Daytime is when the sun is shining the earth that faces away from the sun is in a shadow (of the earth itself); this is night visibly and night happens when or nighttime. We experience cycles of other objects (e.g., hills, clouds, daytime and nighttime because the earth the moon, night, dark, the rotates once every 24 hours. atmosphere) block the sun from shining. [NOTE: It may help clarify things if we use Daytime and night result from the the word “daytime” to refer to that period of time when the sun is above the horizon sun revolving around the earth and use the word “day” to refer to a period once a day. Daytime and night result from the of 24 hours. In everyday language we often use the word “day” to refer to either earth revolving around the sun of these time frames, which can be once a day. confusing to children.] Daytime and night result from the sun moving up and down. The moon is only or always visible The moon can be visible during the at night. daytime or at nighttime, depending on where it is in its orbit. Considered over the The moon is only rarely visible course of a year, the amount of time that during daytime. the moon is visible during daytime is essentially equal to the amount of time it is visible at nighttime. The moon, earth, and sun are all The earth and moon are on the same relatively similar in size (e.g., the order of magnitude with respect to size. sun may be about twice as big as [The moon’s diameter is about 27% of the the earth and the earth may be earth’s diameter.] about twice as big as the moon). The sun is several orders of magnitude The sun and moon are the same larger than the earth. [The sun’s diameter size (since they each appear to be is roughly 108 times larger than the the same size when we view them diameter of the earth.] in the sky). [This belief is Although the sun is several orders of supported (if we neglect to magnitude bigger than the moon, the sun consider that they are not the and the moon both appear to be about the same distance from the earth) same size when viewed from the earth. when the moon passes in front of This is because the sun, while much the sun during a solar eclipse and bigger, is also much further away from the essentially appears to match the earth than is the moon. size of the sun.] Sun diameter ≈ 1,382,000 km Earth diameter ≈ 12,753 km Moon diameter ≈ 3,474 km Naïve & Goal Conceptions for Sun, Earth, and Moon 2001.08.29 [RTSmith] Revised 2002.09.01 Distances The average distance of the earth from the sun is slightly less than 150,000,000 km. Therefore, the average earth-to-sun distance is equal to approximately 11,730 earth diameters. [The earth is a bit closer to the sun during winter in the northern hemisphere and a bit further away from the sun during summer in the northern hemisphere.] The average distance of the moon from the earth is 384,467 km. Therefore, the average earth-to-moon distance is equal to approximately 30 earth diameters. Distances and The earth is closer to the sun The slight change in the distance of the Seasons during summer and further away earth from the sun as the earth orbits the from the sun during winter. This is sun is an insignificant factor in determining why it is hotter in summer and seasonal changes. In fact, the earth is a colder in winter. bit closer to the sun during winter in the northern hemisphere and a bit further away from the sun during summer in the northern hemisphere. Sun/Earth/Moon The earth is the center of the The sun is at the center of our solar Relative Positions and universe. Both the sun and the system. Nine planets, including the earth, Motions moon go around the earth. plus numerous other objects (e.g., asteroids, comets) orbit the sun. The The moon and the earth each moon orbits the earth. (Several other have separate orbits around the planets also have moons orbiting them.) sun. Our solar system is moving within our [Position and motion are rotating galaxy (i.e., the Milky Way), and absolutes.] our galaxy is also in motion relative to other galaxies (i.e., the rest of the universe). Position and motion are determined relative to some reference frame. FYI: Orbital and The amount of time it takes to make one rotation is called a day, Rotational Periods and for the earth that is equal to 24 hours. The amount of time it takes the earth to orbit the sun is called a year and is equal to slightly more than 365 days. The amount of time it takes the moon to orbit the earth is about 27.3 days. However, since the earth is orbiting the sun while the moon is orbiting the earth, it takes 29.5 days from full moon to full moon, which is called a lunar cycle. A lunar cycle takes slightly less than one month. The moon’s rate of rotation is the same as its rate of revolution; hence the same side of the moon always faces the earth as it orbits the earth. The orbit of the moon is slightly inclined from the plane of the earth’s orbit about the sun (which is why we don’t have an eclipse with every new and full moon). The outer layers of the Sun exhibit “differential rotation.” That means that at the equator the surface rotates once every 25.4 earth days while near the poles one rotation can take as much as 36 earth days. This odd behavior is due to the fact that the Sun is not a solid body like the Earth. The differential rotation extends considerably down into the interior of the Sun, but the core of the Sun rotates as a solid body. Light Sources The moon is a source of light, just Of the sun, earth, and moon, only the sun like the sun (although the sun is emits (or is a source of) light. The side of much brighter). the moon that faces the sun reflects light that strikes it from the sun. We see the moon primarily by this reflected light. Page 3 of 4 Handout #13 The distances between the sun, earth, and moon are on the same order of magnitude as the sizes of the three objects. That is to say, the distance from the earth to the sun or the earth to the moon is equal to a few times the earth’s diameter. Naïve & Goal Conceptions for Sun, Earth, and Moon 2001.08.29 [RTSmith] Revised 2002.09.01 The Sun's Composition and How the Sun Makes Heat and Light Moon Phases Naming the Type of Object FYI: Other Features or Characteristics Page 4 of 4 Handout #13 The sun is on fire, made of flame, burning, producing heat and light by combustion. The sun is mostly composed of hydrogen. The sun releases electromagnetic radiation (including infrared and visible light) by the process of nuclear fusion. The sun is composed of matter that is a "plasma" (i.e., a very hot, ionized gas, which scientists consider to be a distinct, fourth state of matter, different from solids, liquids, and gases). Moon phases are actual changes The side of the moon that faces the sun in the shape of the moon. reflects light from the sun that strikes it. We see the moon primarily by this Moon phases, that is, the changing shape of the observable reflected light. Depending where the moon is in its orbit relative to the sun and the moon from night to night, are earth when we see it, we see more or less caused by the earth’s shadow. of its illuminated surface. As the moon Moon phases, that is, the changing shape of the observable completes one orbit (i.e., over the course of approximately one month), we will see it moon from night to night, are increase and then decrease in terms of caused by clouds. how much of its surface facing us is Moon phases, that is, the illuminated by the sun. This is the changing shape of the observable recurring pattern of lunar phases (from moon from night to night, are new moon to full moon and then back to caused by the sun’s shadow. new moon). Moon phases, that is, the [The earth also reflects light received from changing shape of the observable the sun. Some of this reflected light hits moon from night to night, are the moon and then is reflected back to caused by shadows of other earth. If some of this reflected light strikes planets. the portion of the moon facing earth that is not currently illuminated by the sun, there may still be sufficient light for us to see this portion of the moon, albeit very dimly.] The sun is a planet. The sun is a star. The earth is a planet and it orbits the sun. The moon is a natural satellite of the earth. Sun's mass ≈ 2x1030 kg (about 330,000 times earth) Earth's mass ≈ 6x1024 kg Moon's mass ≈ 7x1022 kg Sun's density ≈ 1.4 g/cm 3 Earth's density ≈ 5.5 g/cm3 Moon's density ≈ 3.4 g/cm3 Sun's surface temperature ≈ 5,500ºC Sun's interior temperature ≈ 14,000,000ºC Earth's average surface temperature ≈ ranges from –89ºC to +58ºC Moon's average surface temperature ≈ ranges from –173ºC to +100ºC The sun and the earth each have a magnetic field; the moon does not. The earth and the moon are essentially “solid”; the sun is an incandescent ball of plasma. Roughly 70% of the earth’s surface is covered by liquid water. (There is no liquid water on the surface of the sun or the moon.) The earth is surrounded by a relatively thin blanket of air, called the “atmosphere.” The moon has no atmosphere. The earth and the moon share some types of surface features, for example, they both have mountains, plains, and craters (although the moon has many more easily visible craters). Naïve & Goal Conceptions for Sun, Earth, and Moon 2001.08.29 [RTSmith] Revised 2002.09.01