This book addresses the significance of light and the observation of electromagnetic radiation for modern astrophysics. It begins by examining the physical properties of light and exploring the question of what light is - wave and/or particle? The reader will learn how to observe the light of distant stars using modern telescopes and what information is contained in the measured electromagnetic spectrum - from X-rays to radio waves. In subsequent chapters, one learns what conclusions can be drawn from light about the temperature, composition, and structure of astrophysical objects. The author also provides a glimpse into the depths and thus the past of the universe. Questions such as: How do we know that the universe is expanding? When did the Big Bang occur? are explored in this investigation of the dark.