Science fiction is defined loosely as fiction that deals with the impact of science and technology on the world. Sometimes the technology is real, sometimes it is entirely imagined and sometimes it has been imagined by an author and then brought to reality by scientists. Science fiction themes often warn of the potential for disaster when technology is abused. One of the earliest science fiction writers was Lucian of Samosata who, around 100 BC, wrote a fantasy about a journey to the moon. Modern science fiction began to take shape in the nineteenth century.