A common belief in Europe during this period was the Aristotelian idea that the world beyond the Moon and planets was immutable. So observers argued that the phenomenon was something in the Earth's atmosphere. However Tycho noted that the object remained stationary from night to night—never changing its parallax—so it must lie far away. He published his observations in the small book "De nova et nullius aevi memoria prius visa stella" (Latin for "Concerning the new and previously unseen star") in 1573. It is from the title of this book that the modern word "nova" for cataclysmic variable stars is derived.