For thousands of years, humans have scanned the sky and charted the movement of celestial bodies. The daily and seasonal patterns of the Sun, Moon, and stars guided sailors home, dictated the timing of planting and harvesting, and became an inspiration for festivals, celebrations, and holidays. The appearance of novae, comets, and storms of ""shooting stars"" lighting up the predawn hours were interpreted as lucky signs, dire omens, or special messages from the gods. These practical and spiritual connections of astronomy with human activity motivated and inspired improvements in observations and technology, which led to a deeper interest in exploring what lies beyond the outskirts of this galaxy and the next. ""Space and Astronomy: Decade by Decade"" reveals how the astronomers unravel the mysteries of how the Sun shines, how stars collapse into black holes, and how the universe expands. It is the story of dreamers who designed rockets to bring back knowledge of other worlds and other galaxies. This volume of the ""Twentieth-Century Science"" set describes the progress of astronomy and the development of spaceflight from 1901 to 2000.