Students plot and analyze NASA data to determine the period of an invisible planet orbiting a wobbling star. By completing this activity, the learner will: explore the motion of a two-body system around a center of mass to better understand how extra-solar planets are discovered. answer reflective questions designed to illustrate that the Sun is not a stationary object. answer questions about the magnitude and direction of the velocity of both the Sun and Jupiter. plot and analyze NASA data to determine the period of an invisible planet orbiting a wobbling star. National Science Education Standards National Mathematics Education Standards Materials and Technology Scientific Background Activity 1: Analyze and answer questions about four drawings that show the positions of the Sun and Jupiter at four different times during a single orbit. Activity 2: View movies of athletes competing in a Hammer Throw and discover facts about the center of mass. Activity 3: Analyze actual scientific data from recent discoveries of extra-solar planets and make plots of the central star's velocity toward or away from an observer versus time in order to determine the period of an invisible planet's orbit. Activity 1: Exploration-The Motion of the Sun Activity Page One allows students to explore the motion of a two-body system around a center of mass to better understand how extra-solar planets are discovered. Students are shown a drawing depicting the orbital motion of the Sun and Jupiter and answer reflective questions designed to illustrate that the Sun is not a stationary object, but that all stars move or wobble when orbited by a large planet. Students then tackle questions about the magnitude and direction of the velocity of both the Sun and Jupiter. Activity 2:Concept Introduction-The Hammer Throw Activity Page Two allows students to view movies of athletes competing in the Hammer Throw. Students discover that the hammer and thrower both move about a common center of mass. They find that the center of mass is determined by considering the positions and masses of the two bodies. Activity 3: Concept Application: Discovering New Planets Activity Page Three allows students to use actual scientific data from recent discoveries of extra-solar planets. By plotting the central star's velocity toward or away from an observer versus time, students determine the period of an invisible planet's orbit. Assessment