National Science Education Standards Grades 5-8 Earth in the Solar System  The earth is the third planet from the sun in a system that includes the moon, the sun, eight other planets and their moons, and smaller objects, such as asteroids and comets.  The sun, and average star, is the central and largest body in the solar system. Most objects in the solar system are in regular and predictable motion.  Those motions explain such phenomena as the day, the year, the phases of the moon, and eclipses. Gravity is the force that keeps planets in orbit around the sun and governs the rest of the motion on the solar system.  Gravity alone holds us to the Earth's surface and explains the phenomena of the tides. The sun is the major source of energy for phenomena on the Earth's surface, such as growth of plants, winds, ocean currents, and the water cycle.  Seasons result from variations in the amount of the Sun's energy hitting the surface, due to the tilt of the Earth's rotation on its axis and the length of the day. Understandings about Science and Technology  Scientific inquiry and technological design have similarities and differences.  Scientists propose explanations for questions about the natural world, and engineers propose solutions relating to human problems, needs, and aspirations.  Technological solutions are temporary; technologies exist within nature and so they cannot contavene physical or biological principles; technological solutions have side effects; and technologies cost, carry risks, and provide benefits. Many different people in different cultures have made and continue to make contributions to science and technology. Science and technology are reciprocal.  Science helps drive technology, as it addresses questions that demand more sophisticated instruments and provides principles for better instrumentation and technique.  Technology is essential to science, because it provides instruments and techniques that enable observations of objects and phenomena that are otherwise unobservable due to factors such as quantity, distance, location, size, and speed.  Technology also provides tools for investigations, inquiry, and analysis. Perfectly designed solutions do not exist.  All technological solutions have tradeoffs, such as safety, cost, efficiency, and appearance.  Engineers often build in back-up systems to provide safety.  Risk is part of living in a highly technological world.  Reducing risk often results in new technology. Technological designs have constraints.  Some constraints are unavoidable; for example, properties of materials, or effects of weather and friction; other constraints limit choices in the desigh, for example, environmental protection, human safety, and aesthetics. Technological solutions have intended benefits and unintended consequences.  Some consequences can be predicted, others cannot.