About the Cover

The Gulf Coast region of Texas is home to some of the best beaches in the country, as well as the space program in Houston. The 72-inch Armillary Sphere, located in Sam Houston Park in Houston, has one large vertical circle representing the meridian of Houston, an inside circle representing the celestial equator, and a rod through the center representing the Earth’s axis. The sphere is designed so the central rod points toward the North Star. You’ll learn more about circles and spheres in Chapters 10, 11, and 12.

3D Lissajous curve. Created with Mathematica. A 3D Lissajous figure is constructed as a tube around a trigonometric space curve. The radius of the tube is made proportional to the distance to the nearest self-intersection. For more information and for programs to construct such graphics, see: www.wolfram.com/r/textbook.