• 6-8: 4A/M3. Nine planets of very different size, composition, and surface features move around the sun in nearly circular orbits. Some planets have a variety of moons and even flat rings of rock and ice particles orbiting around them. Some of these planets and moons show evidence of geologic activity. The earth is orbited by one moon, many artificial satellites, and debris.

• 6-8: 4F/M3b. If a force acts towards a single center, the object's path may curve into an orbit around the center.
• 9-12: 4F/H2. All motion is relative to whatever frame of reference is chosen, for there is no motionless frame from which to judge all motion.

• 9-12: 10A/H1. To someone standing on the earth, it seems as if it is large and stationary and that all other objects in the sky orbit around it. That perception was the basis for theories of how the universe is organized that prevailed for over 2,000 years.
• 9-12: 10A/H2. Ptolemy, an Egyptian astronomer living in the second century A.D., devised a powerful mathematical model of the universe based on continuous motion in perfect circles, and in circles on circles. With the model, he was able to predict the motions of the sun, moon, and stars, and even of the irregular "wandering stars" now called planets.
• 9-12: 10A/H3. In the 1500s, a Polish astronomer named Copernicus suggested that all those same motions could be explained by imagining that the earth was turning around once a day and orbiting around the sun once a year. This explanation was rejected by nearly everyone because it violated common sense and required the universe to be unbelievably large. Worse, it flew in the face of the belief, universally held at the time, that the earth was at the center of the universe.
• 9-12: 10A/H8. The work of Copernicus, Galileo, Brahe, and Kepler eventually changed people's perception of their place in the universe.

• 6-8: 11B/M1. Models are often used to think about processes that happen too slowly, too quickly, or on too small a scale to observe directly. They are also used for processes that are too vast, too complex, or too dangerous to study.
• 6-8: 11B/M3. Different models can be used to represent the same thing. What model to use depends on its purpose.
• 6-8: 11B/M4. Simulations are often useful in modeling events and processes.
• 9-12: 11B/H3. The usefulness of a model can be tested by comparing its predictions to actual observations in the real world. But a close match does not necessarily mean that other models would not work equally well or better.

Explore both the Ptolemaic (geocentric) and Copernican (heliocentric) models of the solar system in this module that features two simulations, comprehensive student guide, pre-test, post-test, and content support for teachers.

• Physics First Astronomy Resources For the High School Classroom Unit
• Conceptual Physics Astronomy Resources For the High School Classroom Unit
• Algebra-Based Physics Astronomy Resources For the High School Classroom Unit
• AP/Calculus-Based Physics Astronomy Resources For the High School Classroom Unit

These simulations explore the universe as envisioned by early thinkers. Explore the Ptolemy's Model (geocentric) and Copernicus' Model (heliocentric). Contains student guide, pretest, post-test, and background info.

• Physics First Astronomy: An Historical Perspective Unit
• Conceptual Physics Astronomy: An Historical Perspective Unit
• Algebra-Based Physics Astronomy: An Historical Perspective Unit
• AP/Calculus-Based Physics Astronomy: An Historical Perspective Unit