Earth's Sun and Atmosphere -- Measuring Atmosphere and Surface Properties -- Instrument Design Principles I: Radiometers -- Instrument Design Principles II: Sun Photometers -- Concluding Remarks. Bringing the Sun Down to Earth is intended for teachers, students, and anyone who wants to understand their environment. It provides a unique perspective to monitoring the role of the sun and Earth's atmosphere in maintaining our planet as a place hospitable to advanced life as we understand it. The book first presents some science background about the sun and Earth's atmosphere and then describes the kinds of measurements that can be made with inexpensive equipment to study how solar radiation interacts with the atmosphere on its way to Earth's surface. Such measurements are critical to understanding the forces that will modify Earth's climate during the 21st century. The book describes in detail how to design, build, calibrate, and use inexpensive instruments for measuring solar radiation, ranging from total radiation from the entire sky to narrow spectral bands of radiation travelling along a path directly from the sun. Students and their teachers will learn a great deal about weather, the seasons, and the atmosphere, and they will develop a much better understanding of how to measure the physical world around them. When these instruments are calibrated and used properly, they can be used for serious research that produces results comparable to data from other ground-based sources provided by the science community.