For thousands of years, humans have been fascinated by what we see in the sky. As time progressed and technology advanced, people were able to investigate further. However, even in the twenty-first century, there is still so much we do not know. Is there another planet out there that can support intelligent life? What are UFOs? What is the real definition of a planet? These and other questions are explored in each volume of this series, giving readers insight into the workings of our mysterious universe.