An early image of a transient: This is a sketch of the Crab Nebula made by the Earl of Rosse in the 19th century. The Crab is the remains of a supernova in our own galaxy that exploded in 1054. See what the Crab nebula looks like today. Image credit: W. Parsons.
The study of transients is nearly as old as astronomy itself. The ancient Greeks knew that the night sky changed – in fact the word "planet" comes from the Greek "planētēs" which means "wanderer", as Mars and Jupiter appeared to wander across the sky.
But the study of transients started in earnest in the 1600s, when the Danish astronomer Tycho Brahe and Johannes Kepler in Germany observed the appearance of a "new star" in the night sky. At the time, people believed that such astronomical changes were bad omens, or would affect the fate of kings and queens. We know now that this is not the case, but we are still just as interested in the changing night sky.