Astronomy Excerpts from the Frameworks for Science Education - Third Grade

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1 NOTE: Since the writing of the Frameworks, Pluto has been reclassified as a dwarf planet along with several other known small bodies of similar size. There are likely to be hundreds more discovered out beyond Pluto, and it seemed silly to keep expanding the number of planets in the solar system with every discovery of another small lump of rock. The solar system therefore has eight official planets. Astronomy Excerpts from the Frameworks for Science Education - Third Grade STANDARD SET 4. Earth Sciences Earth sciences standards in grade three center on the concept that objects in the sky move in regular and predictable patterns. It is important that students know and are familiar with the patterns and movements of the Sun, Moon, and stars, both as those bodies actually move and as they appear to move when viewed from Earth. Seasonal changes correlate with changes in both the amount of daily sunlight and the position of the Sun in the sky. Seasonal changes are caused by the tilt of Earth s axis of rotation and the position of Earth relative to the Sun. Students will also learn about the relationships between the phases of the Moon and the changes in the positions of the Sun and Moon. Using models and telescopes may help students grasp the concepts presented in the standards. 4. Objects in the sky move in regular and predictable patterns. As a basis for understanding this concept: a. Students know the patterns of stars stay the same, although they appear to move across the sky nightly, and different stars can be seen in different seasons. The relative position of stars with respect to each other in the night sky is fixed. The apparent motion of the stars through the night sky is a function of Earth turning on its own axis. Starlike objects do move across the fixed pattern of stars in the night sky, but those stars are really planets. Stars appear stationary relative to one another because they are far outside the solar system. The positions of stars appear to change each season from a particular point of view on Earth because that point will face progressively different parts of the universe at night. The stars that are visible in the summer nighttime sky would be visible in the winter daytime sky if they were bright enough to outshine the Sun. 4. b. Students know the way in which the Moon s appearance changes during the four-week lunar cycle. Students should be taught to observe the phases of the Moon; recognize the pattern of changes; and know such terms as the full, quarter, waxing, waning, and crescent Moon. The reason for this pattern of changes may then be explored. One side of the Moon is always in sunlight (except in the case of an eclipse). How much of the sunlit surface of the Moon will be visible from Earth depends on the relative positions of Earth, the Moon, and the Sun. Earth and the Moon continuously cycle through changes in their positions relative to the Sun; therefore, the Moon will go through phases from new to full depending on how much of its lighted surface is visible from Earth. Models may help in the teaching of the standard. Students may be shown the rotation of Earth on its axis; how the day and night cycle works; and why the Moon, like the Sun, appears to rise and set. Students may also be shown Earth s position relative to the Sun, the Moon s position relative to Earth, and how Earth orbits the Sun once a year. Students can observe the actual position changes in the Moon and in the background star patterns at

2 the same time each night, continuing their observations long enough to include a full lunar cycle. They can be shown how the motion of the Moon around Earth accounts for those observations. 4. c. Students know telescopes magnify the appearance of some distant objects in the sky, including the Moon and the planets. The number of stars that can be seen through telescopes is dramatically greater than the number that can be seen by the unaided eye. Students are often startled the first time they look at details of the Moon through a telescope or even through high-quality binoculars. They quickly come to appreciate how those instruments facilitate the study of very distant objects. With the help of a telescope or very high-powered binoculars, students can see the rings of Saturn and some of the details of other planets. Students must never be permitted to look directly or stare at the Sun with the naked eye through binoculars, telescopes, or any other optical instruments. There are many pictures taken by powerful telescopes of planets, stars, and galaxies that students should have the opportunity to study in books. 4. d. Students know that Earth is one of several planets that orbit the Sun and that the Moon orbits Earth. The patterns of the stars stay the same relative to one another although they appear to move because of the rotation of Earth. Several starlike objects move across the sky s star patterns. They are planets that shine by light reflected from the Sun. Five planets can be seen without the aid of a telescope: Mercury, Venus, Mars, Jupiter, and Saturn. Three can be seen only with the aid of a telescope: Uranus, Neptune, and Pluto. Earth is also a planet and moves about the Sun in a path (orbit) that is similar to that of the other planets. Nine planets are in the solar system. The Moon orbits Earth. Because Earth itself is a planet, measuring the orbits of other planets is a complex process. The process is so complex that scientists took a long time to figure out the different spatial relationships between the Moon, Earth, other planets, and the Sun. 4. e. Students know the position of the Sun in the sky changes during the course of the day and from season to season. During a single day the rotation of Earth causes the position of the Sun to change on the horizon. It may be helpful for students to keep track of the Sun s position and watch how shadows lengthen rapidly as sunset approaches. From season to season the length of day and the angle of the Sun vary. Students should know that they live in the Northern Hemisphere, where the Sun at noon is lower and to the south in the sky in the winter and more directly overhead in the summer. Shorter or longer days and more or less direct sunlight characterize the seasons. The angle of the Sun in the sky at noon and the length of the day vary throughout the year because Earth s axis is tilted in comparison to the plane of its orbit. Astronomy Excerpts from the Frameworks for Science Education - Fifth Grade STANDARD SET 5. Earth Sciences (The Solar System) Student knowledge of the solar system includes an understanding of and the ability to describe the relative motions of the planets. Students already know that Earth orbits the

3 Sun and the Moon orbits Earth. Students in grade five learn the composition of the Sun and that the solar system includes small bodies, such as asteroids and comets, as well as the Sun, nine planets, and their moons. They learn the basic relationship between gravity and the planetary orbits. 5. The solar system consists of planets and other bodies that orbit the Sun in predictable paths. As a basis for understanding this concept: a. Students know the Sun, an average star, is the central and largest body in the solar system and is composed primarily of hydrogen and helium. The Sun is about one million times the volume of Earth. Its mass can be calculated from the shapes of the planetary orbits, which result from the gravitational attraction between the Sun and its planets. The fusion of hydrogen to helium produces most of the Sun s energy. 5. b. Students know the solar system includes the planet Earth, the Moon, the Sun, eight other planets and their satellites, and smaller objects, such as asteroids and comets. The solar system comprises nine planets, in the following order from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. Most of the planets have moons in orbit about them, but only Earth s moon is visible to the unaided eye. Asteroids and comets are small bodies, most of which are in irregular orbits about the Sun. Many science texts and Web sites provide information and photographs of objects in the solar system that are collected from NASA s planetary, comet, and asteroid missions and from the use of Earth and space telescopes. 5. c. Students know the path of a planet around the Sun is due to the gravitational attraction between the Sun and the planet. Planets move in elliptical but nearly circular orbits around the Sun just as the Moon moves in a nearly circular orbit around Earth. Each object in the solar system would move in a straight line if it were not pulled or pushed by a force. Gravity causes a pull, or attraction, between the mass (matter) of each of the planets and the mass (matter) of the Sun. This pull is what continually deflects a planet s path toward the Sun and produces its orbit. Students may wonder why the pull of gravity does not cause the planets to fall into the Sun or the Moon into Earth. One explanation is that the planets and Moon are in fact falling, but they are also moving very fast to the side. As the Moon is pulled toward Earth, it also moves forward creating the curved path of its orbit. Thus the Moon is constantly falling, but the downward and sideways motions are exactly balanced so that the Moon never gets closer to or farther away from Earth. In the same way the planets are maintained in orbits around the Sun. Understanding that gravity exists in outer space may be made more difficult by the images of astronauts floating weightless in their capsules. When these pictures are taken, the astronauts are in orbit around Earth and are essentially free-falling (just like the Moon). Astronomy Excerpts from the Frameworks for Science Education - Eighth Grade 2. g. Students know the role of gravity in forming and maintaining the shapes of planets, stars, and the solar system.

4 Gravity, an attractive force between masses, is responsible for forming the Sun, the planets, and the moons in the solar system into their spherical shapes and for holding the system together. It is also responsible for internal pressures in the Sun, Earth and other planets, and the atmosphere. Earth) unless a force was acting on it to change its direction into a circular path. Direction of force of mutual gravitational attraction of Earth and the Moon The Moon's path with no gravitational attraction Earth Orbital path of the Moon Fig.1. Effect of Gravity on the Moon s Path Newton asked himself whether the force that causes objects to fall to Earth could extend to the Moon. Newton knew that the Moon should travel in a straight line (getting farther and farther from Earth and other planets, and the atmosphere. Newton asked himself whether the force that causes objects to fall to Earth could extend to the Moon. Newton knew that the Moon should travel in a straight line (getting farther and farther from Earth) unless a force was acting on it to change its direction into a circular path. He worked out the mathematics that convinced him that the force between all massive objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers. This relationship was then extended to explain the motion of Earth and other planets about the Sun. Initially, the universe consisted of light elements, such as hydrogen, helium, and lithium, distributed in space. The attraction of every particle of matter for every other particle of matter caused the stars to form, making possible the stuff of the universe. As gravity is the fundamental force responsible for the formation and motion of stars and of the clusters of stars called galaxies, it controls the size and shape of the universe. STANDARD SET 4. Earth in the Solar System (Earth Sciences) Students in grade eight are ready to tackle the larger picture of galaxies and astronomical distances. They are ready to study stars compared with and contrasted to the Sun and to learn in greater detail about the planets and other objects in the solar system. High school studies of earth sciences will include the dimension of time along with three-dimensional space in the study of astronomy. 4. The structure and composition of the universe can be learned from studying stars and galaxies and their evolution. As a basis for understanding this concept: a. Students know galaxies are clusters of billions of stars and may have different shapes. Stars are not uniformly distributed throughout the universe but are clustered by the billions in galaxies. Some of the fuzzy points of light in the sky that were originally thought to be stars are now known to be distant galaxies. Galaxies themselves appear to form clusters that are separated by vast expanses of empty space. As galaxies are discovered they are classified by their differing sizes and shapes. The most common shapes are spiral, elliptical, and irregular. Beautiful, fullcolor photographs of astronomical objects are available on the Internet, in library books, and in

5 popular and professional journals. It may also interest students to know that astronomers have inferred the existence of planets orbiting some stars. 4. b. Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature, and color. The Sun is a star located on the rim of a typical spiral galaxy called the Milky Way and orbits the galactic center. In similar spiral galaxies this galactic center appears as a bulge of stars in the heart of the disk. The bright band of stars cutting across the night sky is the edge of the Milky Way as seen from the perspective of Earth, which lies within the disk of the galaxy. Stars vary greatly in size, temperature, and color. For the most part those variations are related to the stars life cycles. Light from the Sun and other stars indicates that the Sun is a fairly typical star. It has a mass of about kg and an energy output, or luminosity, of about joules/sec. The surface temperature of the Sun is approximately 5,500 degrees Celsius, and the radius of the Sun is about 700 million meters. The surface temperature determines the yellow color of the light shining from the Sun. Red stars have cooler surface temperatures, and blue stars have hotter surface temperatures. To connect the surface temperature to the color of the Sun or of other stars, teachers should obtain a black-body temperature spectrum chart, which is typically found in high school and college textbooks. 4. c. Students know how to use astronomical units and light years as measures of distance between the Sun, stars, and Earth. Distances between astronomical objects are enormous. Measurement units such as centimeters, meters, and kilometers used in the laboratory or on field trips are not useful for expressing those distances. Consequently, astronomers use other units to describe large distances. The astronomical unit (AU) is defined to be equal to the average distance from Earth to the Sun: 1 AU = meters. Distances between planets of the solar system are usually expressed in AU. For distances between stars and galaxies, even that large unit of length is not sufficient. Interstellar and intergalactic distances are expressed in terms of how far light travels in one year, the light year (ly): 1 ly = meters, or approximately 6 trillion miles. The most distant objects observed in the universe are estimated to be 10 to 15 billion light years from the solar system. Teachers need to help students become familiar with AUs by expressing the distance from the Sun to the planets in AUs instead of meters or miles. A good way to become familiar with the relative distances of the planets from the Sun is to lay out the solar system to scale on a length of cash register tape. 4. d. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light. The energy from the Sun and other stars, seen as visible light, is caused by nuclear fusion reactions that occur deep inside the stars cores. By carefully analyzing the spectrum of light from stars, scientists know that most stars are composed primarily of hydrogen, a smaller amount of helium, and much smaller amounts of all the other chemical elements. Most stars are born from the gravitational compression and heating of hydrogen gas. A fusion reaction results when hydrogen nuclei combine to form helium nuclei. This event releases energy and establishes a balance between the inward pull of gravity and the outward pressure of the fusion reaction products. Ancient peoples observed that some objects in the night sky wandered about while other objects maintained fixed positions in relation to one another (i.e., the constellations). Those wanderers

6 are the planets. Through careful observations of the planets movements, scientists found that planets travel in nearly circular (slightly elliptical) orbits about the Sun. Planets (and the Moon) do not generate the light that makes them visible, a fact that is demonstrated during eclipses of the Moon or by observation of the phases of the Moon and planets when a portion is shaded from the direct light of the Sun. Various types of exploratory missions have yielded much information about the reflectivity, structure, and composition of the Moon and the planets. Those missions have included spacecraft flying by and orbiting those bodies, the soft landing of spacecraft fitted with instruments, and, of course, the visits of astronauts to the Moon. 4. e. Students know the appearance, general composition, relative position and size, and motion of objects in the solar system, including planets, planetary satellites, comets, and asteroids. Nine planets are currently known in the solar system: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. They vary greatly in size and appearance. For example, the mass of Earth is kg and the radius is m. Jupiter has more than 300 times the mass of Earth, and the radius is ten times larger. The planets also drastically vary in their distance from the Sun, period of revolution about the Sun, period of rotation about their own axis, tilt of their axis, composition, and appearance. The inner planets (Mercury, Venus, Earth, and Mars) tend to be relatively small and are composed primarily of rock. The outer planets (Jupiter, Saturn, Uranus, and Neptune) are generally much larger and are composed primarily of gas. Pluto is composed primarily of rock and is the smallest planet in the solar system. All the planets are much smaller than the Sun. All objects are attracted toward one another gravitationally, and the strength of the gravitational force between them depends on their masses and the distance that separates them from one another and from the Sun. Before Newton formulated his laws of motion and the law of universal gravitational attraction, German astronomer Johannes Kepler deduced from astronomical observations three laws (Kepler s laws) that describe the motions of the planets. Planets have smaller objects orbiting them called satellites or moons. Earth has one moon that completes an orbit once every 28 days (approximately). Mercury and Venus have no moons, but Jupiter and Saturn have many moons. Very small objects composed mostly of rock (asteroids) or the ice from condensed gases (comets) or both also orbit the Sun. The orbits of many asteroids are relatively circular and lie between the orbital paths of Mars and Jupiter (the asteroid belt). Some asteroids and all comets have highly elliptical orbits, causing them to range great distances from very close to the Sun to well beyond the orbit of Pluto. Teachers should look for field trip opportunities for students to observe the night sky from an astronomical observatory or with the aid of a local astronomical society. A visit to a planetarium would be another way of observing the sky. If feasible, teachers should have students observe the motion of Jupiter s inner moons as well as the phases of Venus. Using resources in the librarymedia center, students can research related topics of interest.