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This interactive is used in Chapter 27. Is it possible that the “wiggle” of a star can tell astronomers about worlds in other star systems? Yes, it is, and this Interactive will show you how. When planets orbit a star, they impact the motion of the star, and by observing that motion, astronomers can infer the presence, mass, and distance of the planet. Things get more complicated when there are multiple planets. Observe Earth’s impact on the Sun’s motion, and you will understand why Earth-type planets around other stars are hard to detect. Compare that to a “Hot Jupiter” and see how much more readily it can be seen. Then observe the multiple planet system to see how its much more complex interactions are reflected on the graph.