21^st Century Astronomy, Second Edition

Chapter 3: Gravity and Orbits—A Celestial Ballet

Study Plan

In this chapter we follow the story of the birth of modern science as humans discovered regular patterns in the motions of the planets, then went on to explain those patterns with fundamental physical laws. Along the way we will explore

• Empirical rules discovered by Kepler that describe the elliptical orbits of planets around the Sun.
• Theoretical physical laws discovered by Newton and Galileo that govern the motion of all objects.
• The use of proportionality to describe patterns and relationships in nature.
• The nature of scientific theories, the roles of empirical and theoretical science, and the difference between science and pseudoscience.
• How Newton’s laws of motion and an inverse square law of gravitation combine to explain an orbit as one body falling freely around another.
• The cosmological principle that grew from the startling realization that the heavens and Earth are governed by the same physical laws.
• How theories lead to new knowledge, such as the way Newton’s derivation of Kepler’s third law is used to measure the masses of objects from observations of orbital motions.

Organize

1. Prepare for lecture by reading the assigned sections from Chapter 3 in your textbook or ebook. This will provide an organizing framework for concepts introduced in lecture, and help you take better notes.
2. Take the Diagnostic Quiz to assess your understanding of the basic concepts and identify gaps in your understanding of the assigned reading.

Learn

1. Access the Animations given for this chapter. These brief lessons enhance your understanding of core concepts:
   Kepler's Laws
   Section: 3.2
   Newton Fires a Shot Heard 'round the World
   Section: 3.5
2. Use the FlashCards to test your memory for new terms.
3. Review Foundations Box 3.1 on Proportionality and Box 3.2 on Circular Velocity.
4. Work the “Thinking about the Concepts” and “Applying the Concepts” questions in the end of chapter review materials.
5. If your instructor has assigned SmartWork online homework, login from the right navigation pane for additional practice and review.

Connect

1. Periodic Connections boxes and the Seeing the Forest through the Trees section at the chapter’s end draw your attention to recurring themes and help prepare you for concepts explored more fully in subsequent chapters.
2. Visit Astronomy in the News for breaking news of new discoveries and the opportunity to apply what you’ve learned in this chapter to real-world (and real Universe) events.

Instructors now have an easy way to collect students’ online quizzes with the Norton Gradebook without flooding their inboxes with e-mails.

Students can track their online quiz scores by setting up their own Student Gradebook.